yabasic(1)

NAME
yabasic - yet another Basic

SYNOPSIS
yabasic [OPTIONS] [FILENAME [ARGUMENTS]]

DESCRIPTION
Yabasic implements the most common and simple elements of the basic language. It comes with goto/gosub, with various loops, with user defined subroutines and libraries. Yabasic does simple graphics and printing. Yabasic runs under Unix and Windows, it is small, open source and free. This man-page is derived from yabasic.htm, which too should be installed on your system; per default in /usr/local/share/applications/yabasic/yabasic.htm. The same information can also be found on www.yabasic.de Here is its content:
 Yabasic

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 Table of Contents

 1. Introduction

     About this document
     About yabasic

 2. The yabasic-program under Windows

     Starting yabasic
     Options
     The context Menu

 3. The yabasic-program under Unix

     Starting yabasic
     Options
     Setting defaults

 4. Command line options of yabasic
 5. Some features of yabasic, explained by topic

     print, input and others
     Control statements: loops, if and switch
     Drawing and painting
     Reading from and writing to files
     Subroutines and Libraries
     String processing
     Arithmetic and numbers
     Data and such
     Other interesting commands.

 6. All commands and functions of yabasic listed by topic

     Number processing and conversion
     Conditions and control structures
     Data keeping and processing
     String processing
     File operations and printing
     Subroutines and libraries
     Other commands
     Graphics and printing

 7. All commands and functions of yabasic grouped alphabetically

     A
     B
     C
     D
     E
     F
     G
     H
     I
     L
     M
     N
     O
     P
     R
     S
     T
     U
     V
     W
     X
     Special characters
     Reserved Words

 8. Some general concepts and terms

     Logical shortcuts
     Conditions and expressions
     References on arrays
     Specifying Filenames under Windows
     Escape-sequences
     Creating a standalone program from your yabasic-program

 9. A few example programs

     A very simple program
     The demo of yabasic

 10. The Copyright of yabasic

 Chapter 1. Introduction

 About this document
 About yabasic

 About this document

 This document describes yabasic. You will find information about the yabasic
 interpreter (the program yabasic under Unix or yabasic.exe under Windows) as
 well as the language (which is, of course, a sort of basic) itself.

 This document applies to version 2.82 of yabasic

 However, this document does not contain the latest news about yabasic or a FAQ.
 As such information tends to change rapidly, it is presented online only at
 www.yabasic.de.

 Although basic has its reputation as a language for beginning programmers, this
 is not an introduction to programming at large. Rather this text assumes, that
 the reader has some (moderate) experience with writing and starting computer
 programs.

 About yabasic

 yabasic is a traditional basic interpreter. It understands most of the typical
 basic-constructs, like goto, gosub, line numbers, read, data or
 string-variables with a trailing '$'. But on the other hand, yabasic implements
 some more advanced programming-constructs like subroutines or libraries (but
 not objects). yabasic works much the same under Unix and Windows.

 yabasic puts emphasis on giving results quickly and easily; therefore simple
 commands are provided to open a graphic window, print the graphics or control
 the console screen and get keyboard or mouse information. The example below
 opens a window, draws a circle and prints the graphic:

 open window 100,100
 open printer
 circle 50,50,40
 text 10,50,"Press any key to get a printout"
 clear screen
 inkey$
 close printer
 close window

 This example has fewer lines, than it would have in many other programming
 languages. In the end however yabasic lacks behind more advanced and modern
 programming languages like C++ or Java. But as far as it goes it tends to give
 you results more quickly and easily.

 Chapter 2. The yabasic-program under Windows

 Starting yabasic
 Options
 The context Menu

 Starting yabasic

 Once, yabasic has been set up correctly, there are three ways to start it:

  1. Right click on your desktop: The desktop menu appears with a submenu named
     new. From this submenu choose yabasic. This will create a new icon on your
     desktop. If you right click on this icon, its context menu will appear;
     choose Execute to execute the program.

  2. As a variant of the way described above, you may simply create a file with
     the ending .yab (e.g. with your favorite editor). Everything else then
     works as described above.

  3. From the start-menu: Choose yabasic from your start-menu. A console-window
     will open and you will be asked to type in your program. Once you are
     finished, you need to type return twice, and yabasic will parse and execute
     your program.

     Note

     This is not the preferred way of starting yabasic ! Simply because the
     program, that you have typed, can not be saved and will be lost inevitably
     ! There is no such thing as a save-command and therefore no way to conserve
     the program, that you have typed. This mode is only intended for quick
     hacks, and short programs.

 Options

 Under Windows yabasic will mostly be invoked by double-clicking on an
 appropriate icon; this way you do not have a chance to specify any of the
 command line options below. However, advanced users may change the librarypath
 in the registry, which has the same effect as specifying it as an option on the
 command line.

 See the chapter on options for a complete list of all options, either on Unix
 or Windows.

 The context Menu

 Like every other icon under Windows, the icon of every yabasic-program has a
 context menu offering the most frequent operations, that may be applied to a
 yabasic-program.

 Execute

     This will invoke yabasic to execute your program. The same happens, if you
     double click on the icon.

 Edit

     notepad will be invoked, allowing you to edit your program.

 View docu

     This will present the embedded documentation of your program. Embedded
     documentation is created with the special comment doc.

 Chapter 3. The yabasic-program under Unix

 Starting yabasic
 Options
 Setting defaults

 Starting yabasic

 If your system administrator (vulgo root) has installed yabasic correctly,
 there are three ways to start it:

  1. You may use your favorite editor (emacs, vi ?) to put your program into a
     file (e.g. foo). Make sure that the very first line starts with the
     characters '#!' followed by the full pathname of yabasic (e.g. '#!/usr/
     local/bin/yabasic'). This she-bang-line ensures, that your Unix will invoke
     yabasic to execute your program (see also the entry for the hash
     -character). Moreover, you will need to change the permissions of your
     yabasic-program foo, e.g. chmod u+x foo. After that you may invoke yabasic
     to invoke your program by simply typing foo (without even mentioning
     yabasic). However, if your PATH-variable does not contain a single dot
     ('.') you will have to type the full pathname of your program: e.g. /home/
     ihm/foo (or at least ./foo).

  2. Save your program into a file (e.g. foo) and type yabasic foo. This
     assumes, that the directory, where yabasic resides, is contained within
     your PATH-variable.

  3. Finally your may simply type yabasic (maybe it will be necessary to include
     its full pathname). This will make yabasic come up and you will be asked to
     type in your program. Once you are finished, you need to type return twice,
     and yabasic will parse and execute your program.

     Note

     This is not the preferred way of starting yabasic ! Simply because the
     program, that you have typed, can not be saved and will be lost inevitably
     ! There is no such thing as a save-command and therefore no way to conserve
     the program, that you have typed. This mode is only intended for quick
     hacks, and short programs, i.e. for using yabasic as some sort of fancy
     desktop calculator.

 Options

 yabasic accepts a number of options on the command line.

 See chapter on options for a complete list of all options, either on Unix or
 Windows.

 Setting defaults

 If you want to set some options once for all, you may put them into your
 X-Windows resource file. This is usually the file .Xresources or some such
 within your home directory (type man X for details).

 Here is a sample section, which may appear within this file:

 yabasic*foreground: blue
 yabasic*background: gold
 yabasic*geometry: +10+10
 yabasic*font: 9x15

 This will set the foreground color of the graphic-window to blue and the
 background color to gold. The window will appear at position 10,10 and the text
 font will be 9x15.

 Chapter 4. Command line options of yabasic

 Here are the options, that yabasic accepts on the command line (both under Unix
 and Windows).

 All the options below may be abbreviated (and one hyphen may be dropped), as
 long as the abbreviation does not become ambiguous. For example, you may write
 -e instead of --execute.

 --help or -?

     Prints a short help message, which itself describes two further
     help-options.

 --version

     Prints the version of yabasic.

 --infolevel INFOLEVEL

     Change the infolevel of yabasic, where INFOLEVEL can be one of debug, note,
     warning, error, fatal and bison (the default is warning). This option
     changes the amount of debugging-information yabasic produces. However,
     normally only the author of yabasic (me !) would want to change this.

 --execute A-PROGRAM-AS-A-SINGLE-STRING

     With this option you may specify some yabasic-code to be executed right
     away. This is useful for very short programs, which you do not want to save
     to a file. If this option is given, yabasic will not read any code from a
     file. E.g.

     yabasic -e 'for a=1 to 10:print a*a:next a'

     prints the square numbers from 1 to 10.

 --bind NAME-OF-STANDALONE-PROGRAM

     Create a standalone program (whose name is specified by
     NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on
     the command line. See the section about creating a standalone-program for
     details.

 --geometry +X-POSITION+Y-POSITION

     Sets the position of the graphic window, that is opened by open window (the
     size of this window, of course, is specified within the open
     window-command). An example would be -geometry +20+10, which would place
     the graphic window 10 pixels below the upper border and 20 pixels right of
     the left border of the screen. This value cannot be changed, once yabasic
     has been started.

 -fg FOREGROUND-COLOR or --foreground FOREGROUND-COLOR

     Unix only. Define the foreground color for the graphics-window (that will
     be opened with open window). The usual X11 color names, like red, green, ?
     are accepted. This value cannot be changed, once yabasic has been started.

 -bg BACKGROUND-COLOR or --background BACKGROUND-COLOR

     Unix only. Define the background color for the graphics-window. The usual
     X11 color names are accepted. This value cannot be changed, once yabasic
     has been started.

 --display X11-DISPLAY-SPECIFICATION

     Unix only. Specify the display, where the graphics window of yabasic should
     appear. Normally this value will be already present within the environment
     variable DISPLAY.

 --font NAME-OF-FONT

     Under Unix. Name of the font, which will be used for text within the
     graphics window.

 --font NAME-OF-FONT

     Under Windows. Name of the font, which will be used for graphic-text; can
     be any of decorative, dontcare, modern, roman, script, swiss. You may
     append a fontsize (measured in pixels) to any of those fontnames; for
     example -font swiss30 chooses a swiss-type font with a size of 30 pixels.

 --docu NAME-OF-A-PROGRAM

     Print the embedded documentation of the named program. The embedded
     documentation of a program consists of all the comments within the program,
     which start with the special keyword doc. This documentation can also be
     seen by choosing the corresponding entry from the context-menu of any
     yabasic-program.

 --check

     Check for possible compatibility problems within your yabasic-program. E.g.
     this option reports, if you are using a function, that has recently
     changed.

 --librarypath DIRECTORY-WITH-LIBRARIES

     Change the directory, wherein libraries will be searched and imported (with
     the import-command). See also import for more information about the way,
     libraries are searched.

 --

     Do not try to parse any further options; rather pass the subsequent words
     from the commandline to yabasic.

 Chapter 5. Some features of yabasic, explained by topic

 print, input and others
 Control statements: loops, if and switch
 Drawing and painting
 Reading from and writing to files
 Subroutines and Libraries
 String processing
 Arithmetic and numbers
 Data and such
 Other interesting commands.

 This chapter has sections for some of the major features of yabasic and names a
 few commands related with each area. So, depending on your interest, you find
 the most important commands of this area named; the other commands from this
 area may then be discovered through the links in the see also-section.

 print, input and others

 The print-command is used to put text on the text screen. Here, the term text
 screen stands for your terminal (under Unix) or the console window (under
 Windows).

 At the bottom line, print simply outputs its argument to the text window.
 However, once you have called clear screen you may use advanced features like
 printing colors or copying areas of text with getscreen$ or putscreen.

 You may ask the user for input with the input-command; use inkey$ to get each
 key as soon as it is pressed.

 Control statements: loops, if and switch

 Of course, yabasic has the goto- and gosub-statements; you may go to a label or
 a line number (which is just a special kind of label). goto, despite its bad
 reputation ([goto considered harmful]), has still its good uses; however in
 many cases you are probably better off with loops like repeat-until, while-wend
 or do-loop; you may leave any of these loops with the break-statement or start
 the next iteration immediately with continue.

 Decisions can be made with the if-statement, which comes either in a short and
 a long form. The short form has no then-keyword and extends up to the end of
 the line. The long form extends up to the final endif and may use some of the
 keywords then (which introduces the long form), else or elsif.

 If you want to test the result of an expression against many different values,
 you should probably use the switch-statement.

 Drawing and painting

 You need to call open window before you may draw anything with either line,
 circle, rectangle or triangle; all of these statements may be decorated with
 clear or fill. If you want to change the colour for drawing, use colour. Note
 however, that there can only be a single window open at any given moment in
 time.

 Everything you have drawn can be send to your printer too, if you use the open
 printer command.

 To allow for some (very) limited version of animated graphics, yabasic offers
 the commands getbit$ and putbit, which retrieve rectangular regions from the
 graphics-window into a string or vice versa.

 If you want to sense mouse-clicks, you may use the inkey$-function.

 Reading from and writing to files

 Before you may read or write a file, you need to open it; once you are done,
 you should close it. Each open file is designated by a simple number, which
 might be stored within a variable and must be supplied if you want to access
 the file. This is simply done by putting a hash ('#') followed by the number of
 the file after the keyword input (for reading from) or print (for writing to a
 file) respectively.

 If you need more control, you may consider reading and writing one byte at a
 time, using the multi-purpose commands peek and poke.

 Subroutines and Libraries

 The best way to break any yabasic-program into smaller, more manageable chunks
 are subroutines and libraries. They are yabasic's most advanced means of
 structuring a program.

 Subroutines are created with the command sub. they accept parameters and may
 return a value. Subroutines can be called much like any builtin function of
 yabasic; therefore they allow one to extend the language itself.

 Once you have created a set of related subroutines and you feel that they could
 be useful in other programs too, you may collect them into a library. Such a
 library is contained within a separate file and may be included in any of your
 programs, using the keyword import, which see.

 String processing

 yabasic has a set of functions to extract parts from a string: left$, mid$ and
 right$. Note, that all of them can be assigned to, i.e. they may change part of
 a string.

 If you want to split a string into tokens you should use the functions token or
 split.

 Some functions are handy for normalizing a string: upper$ and lower$ convert a
 string to all upper or lower case respectively, whereas chomp$ cuts of any
 trailing newline character, but only if present.

 chr$ and str$ convert a string into a number, both in different ways.

 To analyze a string use instr (finding one string within the other) or glob
 (testing a string against a simple pattern).

 To concatenate strings use the operator + like in a$ + b$.

 You may also see the complete list of a string processing functions.

 Arithmetic and numbers

 Yabasic handles numbers and arithmetic: You may calculate trigonometric
 functions like sin or atan, or logarithms (with log). Bitwise operations, like
 and or or are available as well min or max (calculate the minimum or maximum of
 its argument) or mod or int (reminder of a division or integer part or a
 number).

 Conversion between numerical bases can be done with hex$ and dec. And you may
 write hexadecimal constants in the usual way, e.g.

 print 0xff

 . All calculations in yabasic are done with double precision.

 Data and such

 You may store data within your program within data-statements; during execution
 you will probably want to read it into arrays, which must have been dimed
 before.

 Other interesting commands.

   * Yabasic programs may start other programs with the commands system and
     system$.

   * peek and poke allow one to get and set internal information; either for the
     operating system (i.e. Unix or Windows) or yabasic itself.

   * The current time or date can be retrieved with (guess what !) time$ and
     date$.

 Chapter 6. All commands and functions of yabasic listed by topic

 Number processing and conversion
 Conditions and control structures
 Data keeping and processing
 String processing
 File operations and printing
 Subroutines and libraries
 Other commands
 Graphics and printing

 Number processing and conversion

 abs()
     returns the absolute value of its numeric argument
 acos()
     returns the arcus cosine of its numeric argument
 and()
     the bitwise arithmetic and
 asin()
     returns the arcus sine of its numeric argument
 atan()
     returns the arctangent of its numeric argument
 bin$()
     converts a number into a sequence of binary digits
 cos()
     return the cosine of its single argument
 dec()
     convert a base 2 or base 16 number into decimal form
 eor()
     compute the bitwise exclusive or of its two arguments
 euler
     another name for the constant 2.71828182864
 exp()
     compute the exponential function of its single argument
 frac()
     return the fractional part of its numeric argument
 int()
     return the integer part of its single numeric argument
 ceil()
     return the smallest integral number, that is greater or equal than its
     argument
 floor()
     return the largest integral number, that is smaller or equal than its
     argument
 log()
     compute the natural logarithm
 max()
     return the larger of its two arguments
 min()
     return the smaller of its two arguments
 mod
     compute the remainder of a division
 or()
     arithmetic or, used for bit-operations
 pi
     a constant with the value 3.14159
 ran()
     return a random number
 sig()
     return the sign of its argument
 sin()
     return the sine of its single argument
 sqr()
     compute the square of its argument
 sqrt()
     compute the square root of its argument
 tan()
     return the tangent of its argument
 xor()
     compute the exclusive or
 ** or ^
     raise its first argument to the power of its second

 Conditions and control structures

 and
     logical and, used in conditions
 break
     breaks out of a switch statement or a loop
 case
     mark the different cases within a switch-statement
 continue
     start the next iteration of a for-, do-, repeat- or while-loop
 default
     mark the default-branch within a switch-statement
 do
     start a (conditionless) do-loop
 else
     mark an alternative within an if-statement
 elsif
     starts an alternate condition within an if-statement
 end
     terminate your program
 endif
     ends an if-statement
 false
     a constant with the value of 0
 fi
     another name for endif
 for
     starts a for-loop
 gosub
     continue execution at another point within your program (and return later)
 goto
     continue execution at another point within your program (and never come
     back)
 if
     evaluate a condition and execute statements or not, depending on the result
 label
     mark a specific location within your program for goto, gosub or restore
 loop
     marks the end of an infinite loop
 next
     mark the end of a for loop
 not
     negate an expression; can be written as !
 on gosub
     jump to one of multiple gosub-targets
 on goto
     jump to one of many goto-targets
 on interrupt
     change reaction on keyboard interrupts
 logical or
     logical or, used in conditions
 pause
     pause, sleep, wait for the specified number of seconds
 repeat
     start a repeat-loop
 return
     return from a subroutine or a gosub
 sleep
     pause, sleep, wait for the specified number of seconds
 switch
     select one of many alternatives depending on a value
 then
     tell the long from the short form of the if-statement
 true
     a constant with the value of 1
 until
     end a repeat-loop
 wait
     pause, sleep, wait for the specified number of seconds
 wend
     end a while-loop
 while
     start a while-loop
 :
     separate commands from each other

 Data keeping and processing

 arraydim()
     returns the dimension of the array, which is passed as an array reference
 arraysize()
     returns the size of a dimension of an array
 data
     introduces a list of data-items
 dim
     create an array prior to its first use
 read
     read data from data-statements
 redim
     create an array prior to its first use. A synonym for dim
 restore
     reposition the data-pointer

 String processing

 asc()
     accepts a string and returns the position of its first character within the
     ascii charset
 chomp$()
     Chop of the trailing newline of its string-argument; if the string does not
     end in a newline, the string is returned unchanged
 chr$()
     accepts a number and returns the character at this position within the
     ascii charset
 glob()
     check if a string matches a simple pattern
 hex$()
     convert a number into hexadecimal
 instr()
     searches its second argument within the first; returns its position if
     found
 left$()
     return (or change) left end of a string
 len()
     return the length of a string
 lower$()
     convert a string to lower case
 ltrim$()
     trim spaces at the left end of a string
 mid$()
     return (or change) characters from within a string
 right$()
     return (or change) the right end of a string
 split()
     split a string into many strings
 str$()
     convert a number into a string
 token()
     split a string into multiple strings
 trim$()
     remove leading and trailing spaces from its argument
 upper$()
     convert a string to upper case
 val()
     converts a string to a number

 File operations and printing

 at()
     can be used in the print-command to place the output at a specified
     position
 beep
     ring the bell within your computer; a synonym for bell
 bell
     ring the bell within your computer (just as beep)
 clear screen
     erases the text window
 close
     close a file, which has been opened before
 close printer
     stops printing of graphics
 print color
     print with color
 print colour
     see print color
 eof
     check, if an open file contains data
 getscreen$()
     returns a string representing a rectangular section of the text terminal
 inkey$
     wait, until a key is pressed
 input
     read input from the user (or from a file) and assign it to a variable
 line input
     read in a whole line of text and assign it to a variable
 open
     open a file
 open printer
     open printer for printing graphics
 print
     Write to terminal or file
 putscreen
     draw a rectangle of characters into the text terminal
 reverse
     print reverse (background and foreground colors exchanged)
 screen
     as clear screen clears the text window
 seek()
     change the position within an open file
 tell
     get the current position within an open file
 using
     Specify the format for printing a number
 #
     either a comment or a marker for a file-number
 @
     synonymous to at
 ;
     suppress the implicit newline after a print-statement

 Subroutines and libraries

 end sub
     ends a subroutine definition
 export
     mark a function as globally visible
 import
     import a library
 local
     mark a variable as local to a subroutine
 numparams
     return the number of parameters, that have been passed to a subroutine
 return
     return from a subroutine or a gosub
 static
     preserves the value of a variable between calls to a subroutine
 step
     specifies the increment step in a for-loop
 sub
     declare a user defined subroutine

 Other commands

 bind()
     Binds a yabasic-program and the yabasic-interpreter together into a
     standalone program.
 compile
     compile a string with yabasic-code on the fly
 date$
     returns a string with various components of the current date
 doc
     special comment, which might be retrieved by the program itself
 docu$
     special array, containing the contents of all docu-statement within the
     program
 error
     raise an error and terminate your program
 execute$()
     execute a user defined subroutine, which must return a string
 execute()
     execute a user defined subroutine, which must return a number
 exit
     terminate your program
 pause
     pause, sleep, wait for the specified number of seconds
 peek
     retrieve various internal information
 peek$
     retrieve various internal string-information
 poke
     change selected internals of yabasic
 rem
     start a comment
 sleep
     pause, sleep, wait for the specified number of seconds
 system()
     hand a statement over to your operating system and return its exitcode
 system$()
     hand a statement over to your operating system and return its output
 time$
     return a string containing the current time
 to
     this keyword appears as part of other statements
 wait
     pause, sleep, wait for the specified number of seconds
 //
     starts a comment
 :
     separate commands from each other

 Graphics and printing

 backcolor
     specify the colour for subsequent drawing of the background
 box
     draw a rectangle. A synonym for rectangle
 circle
     draws a circle in the graphic-window
 clear
     Erase circles, rectangles or triangless
 clear window
     clear the graphic window and begin a new page, if printing is under way
 close curve
     close a curve, that has been drawn by the line-command
 close window
     close the graphics-window
 colour
     specify the colour for subsequent drawing
 dot
     draw a dot in the graphic-window
 fill
     draw a filled circles, rectangles or triangles
 getbit$()
     return a string representing the bit pattern of a rectangle within the
     graphic window
 line
     draw a line
 mouseb
     extract the state of the mousebuttons from a string returned by inkey$
 mousemod
     return the state of the modifier keys during a mouseclick
 mousex
     return the x-position of a mouseclick
 mousey
     return the y-position of a mouseclick
 new curve
     start a new curve, that will be drawn with the line-command
 open window
     open a graphic window
 putbit
     draw a rectangle of pixels into the graphic window
 rectangle
     draw a rectangle
 triangle
     draw a triangle
 text
     write text into your graphic-window
 window origin
     move the origin of a window

 Chapter 7. All commands and functions of yabasic grouped alphabetically

 A
 B
 C
 D
 E
 F
 G
 H
 I
 L
 M
 N
 O
 P
 R
 S
 T
 U
 V
 W
 X
 Special characters
 Reserved Words

 A

 abs() ? returns the absolute value of its numeric argument
 acos() ? returns the arcus cosine of its numeric argument
 and ? logical and, used in conditions
 and() ? the bitwise arithmetic and
 arraydim() ? returns the dimension of the array, which is passed as an array
     reference
 arraysize() ? returns the size of a dimension of an array
 asc() ? accepts a string and returns the position of its first character within
     the ascii charset
 asin() ? returns the arcus sine of its numeric argument
 at() ? can be used in the print-command to place the output at a specified
     position
 atan() ? returns the arctangent of its numeric argument

 Name

 abs() ? returns the absolute value of its numeric argument

 Synopsis

 y=abs(x)

 Description

 If the argument of the abs-function is positive (e.g. 2) it is returned
 unchanged, if the argument is negative (e.g. -1) it is returned as a positive
 value (e.g. 1).

 Example

 print abs(-2),abs(2)

 This example will print 2 2

 See also

 sig

 -------------------------------------------------------------------------------

 Name

 acos() ? returns the arcus cosine of its numeric argument

 Synopsis

 x=acos(angle)

 Description

 acos is the arcus cosine-function, i.e. the inverse of the cos-function. Or,
 more elaborate: It Returns the angle (in radians, not degrees !), which, fed to
 the cosine-function will produce the argument passed to the acos-function.

 Example

 print acos(0.5),acos(cos(pi))

 This example will print 1.0472 3.14159 which are ?/3 and ? respectively.

 See also

 cos, asin

 -------------------------------------------------------------------------------

 Name

 and ? logical and, used in conditions

 Synopsis

 if (a and b) ?
 while (a and b) ?

 Description

 Used in conditions (e.g within if, while or until) to join two expressions.
 Returns true, if and only if its left and right argument are both true and
 false otherwise.

 Note, that logical shortcuts may take place.

 Example

 input "Please enter a number" a
 if (a>=1 and a<=9) print "your input is between 1 and 9"

 See also

 or,not

 -------------------------------------------------------------------------------

 Name

 and() ? the bitwise arithmetic and

 Synopsis

 x=and(a,b)

 Description

 Used to compute the bitwise and of both its argument. Both arguments are
 treated as binary numbers (i.e. a series of 0 and 1); a bit of the resulting
 value will then be 1, if both arguments have a 1 at this position in their
 binary representation.

 Note, that both arguments are silently converted to integer values and that
 negative numbers have their own binary representation and may lead to
 unexpected results when passed to and.

 Example

 print and(6,3)

 This will print 2. This result is clear, if you note, that the binary
 representation of 6 and 3 are 110 and 011 respectively; this will yield 010 in
 binary representation or 2 as decimal.

 See also

 or, eor and not

 -------------------------------------------------------------------------------

 Name

 arraydim() ? returns the dimension of the array, which is passed as an array
 reference

 Synopsis

 a=arraydim(b())

 Description

 If you apply the arraydim()-function on a one-dimensional array (i.e. a vector)
 it will return 1, on a two-dimensional array (i.e. a matrix) it will return 2,
 and so on.

 This is mostly used within subroutines, which expect an array among their
 parameters. Such subroutines tend to use the arraydim-function to check, if the
 array which has been passed, has the right dimension. E.g. a subroutine to
 multiply two matrices may want to check, if it really is invoked with two
 2-dimensional arrays.

 Example

 dim a(10,10),b(10)
 print arraydim(a()),arraydim(b())

 This will print 2 1, which are the dimension of the arrays a() and b(). You may
 check out the function arraysize for a full-fledged example.

 See also

 arraysize and dim.

 -------------------------------------------------------------------------------

 Name

 arraysize() ? returns the size of a dimension of an array

 Synopsis

 x=arraysize(a(),b)

 Description

 The arraysize-function computes the size of a specified dimension of a
 specified array. Here, size stands for the maximum number, that may be used as
 an index for this array. The first argument to this function must be an
 reference to an array, the second one specifies, which of the multiple
 dimensions of the array should be taken to calculate the size.

 An Example involving subroutines: Let's say, an array has been declared as dim
 a(10,20) (that is a two-dimensional array or a matrix). If this array is passed
 as an array reference to a subroutine, this sub will not know, what sort of
 array has been passed. With the arraydim-function the sub will be able to find
 the dimension of the array, with the arraysize-function it will be able to find
 out the size of this array in its two dimensions, which will be 10 and 20
 respectively.

 Our sample array is two dimensional; if you envision it as a matrix this matrix
 has 10 lines and 20 columns (see the dim-statement above. To state it more
 formally: The first dimension (lines) has a size of 10, the second dimension
 (columns) has a size of 20; these numbers are those returned by arraysize(a
 (),1) and arraysize(a(),2) respectively. Refer to the example below for a
 typical usage.

 Example

 rem
 rem  This program adds two matrices elementwise.
 rem

 dim a(10,20),b(10,20),c(10,20)

 rem  initialization of the arrays a() and b()
 for y=1 to 10:for x=1 to 20
    a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
 next x:next y

 matadd(a(),b(),c())

 print "Result:"
 for x=1 to 20
    for y=10 to 1 step -1
       print c(y,x)," ";
    next y
    print
 next x

 sub matadd(m1(),m2(),r())

    rem  This sub will add the matrices m1() and m2()
    rem  elementwise and store the result within r()
    rem  This is not very useful but easy to implement.
    rem  However, this sub excels in checking its arguments
    rem  with arraydim() and arraysize()

    local x:local y

    if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
       error "Need two dimensional arrays as input"
    endif

    y=arraysize(m1(),1):x=arraysize(m1(),2)
    if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
       error "The two matrices cannot be added elementwise"
    endif

    if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
       error "The result cannot be stored in the third argument"
    endif

    local xx:local yy
    for xx=1 to x
       for yy=1 to y
          r(yy,xx)=m1(yy,xx)+m2(yy,xx)
       next yy
    next xx

  end sub

 See also

 arraydim and dim.

 -------------------------------------------------------------------------------

 Name

 asc() ? accepts a string and returns the position of its first character within
 the ascii charset

 Synopsis

 a=asc(char$)

 Description

 The asc-function accepts a string, takes its first character and looks it up
 within the ascii-charset; this position will be returned. The asc-function is
 the opposite of the chr$-function. There are valid uses for asc, however,
 comparing strings (i.e. to bring them into alphabetical sequence) is not among
 them; in such many cases you might consider to compare strings directly with <,
 = and > (rather than converting a string to a number and comparing this
 number).

 Example

 input "Please enter a letter between 'a' and 'y': " a$
 if (a$<"a" or a$>"y") print a$," is not in the proper range":end
 print "The letter after ",a$," is ",chr$(asc(a$)+1)

 See also

 chr$

 -------------------------------------------------------------------------------

 Name

 asin() ? returns the arcus sine of its numeric argument

 Synopsis

 angle=asin(x)

 Description

 acos is the arcus sine-function, i.e. the inverse of the sin-function. Or, more
 elaborate: It Returns the angle (in radians, not degrees !), which, fed to the
 sine-function will produce the argument passed to the asin-function.

 Example

 print asin(0.5),asin(sin(pi))

 This will print 0.523599 -2.06823e-13 which is ? and almost 0 respectively.

 See also

 sin, acos

 -------------------------------------------------------------------------------

 Name

 at() ? can be used in the print-command to place the output at a specified
 position

 Synopsis

 clear screen
 ?
 print at(a,b)
 print @(a,b)

 Description

 The at-clause takes two numeric arguments (e.g. at(2,3)) and can be inserted
 after the print-keyword. at() can be used only if clear screen has been
 executed at least once within the program (otherwise you will get an error).

 The two numeric arguments of the at-function may range from 0 to the width of
 your terminal minus 1, and from 0 to the height of your terminal minus 1; if
 any argument exceeds these values, it will be truncated accordingly. However,
 yabasic has no influence on the size of your terminal (80x25 is a common, but
 not mandatory), the size of your terminal and the maximum values acceptable
 within the at-clause may vary. To get the size of your terminal you may use the
 peek-function: peek("screenwidth") returns the width of your terminal and peek
 ("screenheight") its height.

 Example

 clear screen
 maxx=peek("screenwidth")-1:maxy=peek("screenheight")-1
 for x=0 to maxx
   print at(x,maxy*(0.5+sin(2*pi*x/maxx)/2)) "*"
 next x

 This example plots a full period of the sine-function across the screen.

 See also

 print, clear screen, color

 -------------------------------------------------------------------------------

 Name

 atan() ? returns the arctangent of its numeric argument

 Synopsis

 angle=atan(a,b)
 angle=atan(a)

 Description

 atan is the arctangent-function, i.e. the inverse of the tan-function. Or, more
 elaborate: It Returns the angle (in radians, not degrees !), which, fed to the
 tan-function will produce the argument passed to the atan-function.

 The atan-function has a second form, which accepts two arguments: atan(a,b)
 which is (mostly) equivalent to atan(a/b) except for the fact, that the
 two-argument-form returns an angle in the range -? to ?, whereas the
 one-argument-form returns an angle in the range -?/2 to ?/2. To understand this
 you have to be good at math.

 Example

 print atan(1),atan(tan(pi)),atan(-0,-1),atan(-0,1)

 This will print 0.463648 2.06823e-13 -3.14159 3.14159 which is ?/4, almost 0,
 -? and ? respectively.

 See also

 tan, sin

 B

 backcolor ? change color for background of graphic window
 backcolour ? see backcolor
 beep ? ring the bell within your computer; a synonym for bell
 bell ? ring the bell within your computer (just as beep)
 bin$() ? converts a number into a sequence of binary digits
 bind() ? Binds a yabasic-program and the yabasic-interpreter together into a
     standalone program.
 box ? draw a rectangle. A synonym for rectangle
 break ? breaks out of one or more loops or switch statements

 Name

 color ? change color for background of graphic window

 Synopsis

 backcolour red,green,blue
 backcolour "red,green,blue"

 Description

 Change the color, that becomes visible, if any portion of the window is erased,
 e.g. after clear window or clear line. Note however, that parts of the window,
 that display the old background color will not change.

 As with the color-command, the new background color can either be specified as
 a triple of three numbers or as a single string, that contains those three
 numbers separated by commas.

 Example

 open window 255,255
 for x=10 to 235 step 10:for y=10 to 235 step 10
         backcolour x,y,0
         clear window
         sleep 1
 next y:next x

 This changes the background colour of the graphic window repeatedly and clears
 it every time, so that it is filled with the new background colour.

 See also

 open window, color, line, rectangle, triangle, circle

 -------------------------------------------------------------------------------

 Name

 backcolour ? see backcolor

 Synopsis

 backcolour red,green,blue
 backcolour "red,green,blue"

 See also

 color

 -------------------------------------------------------------------------------

 Name

 beep ? ring the bell within your computer; a synonym for bell

 Synopsis

 beep

 Description

 The bell-command rings the bell within your computer once. This command is not
 a sound-interface, so you can neither vary the length or the height of the
 sound (technically, it just prints ). bell is exactly the same as beep.

 Example

 beep:print "This is a problem ..."

 See also

 beep

 -------------------------------------------------------------------------------

 Name

 bell ? ring the bell within your computer (just as beep)

 Synopsis

 bell

 Description

 The beep-command rings the bell within your computer once. beep is a synonym
 for bell.

 Example

 print "This is a problem ...":beep

 See also

 bell

 -------------------------------------------------------------------------------

 Name

 bin$() ? converts a number into a sequence of binary digits

 Synopsis

 hexadecimal$=bin$(decimal)

 Description

 The bin$-function takes a single numeric argument an converts it into a string
 of binary digits (i.e. zeroes and ones). If you pass a negative number to bin$,
 the resulting string will be preceded by a '-'.

 If you want to convert the other way around (i.e. from binary to decimal) you
 may use the dec-function.

 Example

 for a=1 to 100
   print bin$(a)
 next a

 This example prints the binary representation of all digits between 1 and 100.

 See also

 hex$, dec

 -------------------------------------------------------------------------------

 Name

 bind() ? Binds a yabasic-program and the yabasic-interpreter together into a
 standalone program.

 Synopsis

 bind("foo.exe")

 Description

 The bind-command combines your own yabasic-program (plus all the libraries it
 does import) and the interpreter by copying them into a new file, whose name is
 passed as an argument. This new program may then be executed on any computer,
 even if it does not have yabasic installed.

 Please see the section about creating a standalone-program for details.

 Example

 if (!peek("isbound")) then
   bind "foo"
   print "Successfully created the standalone executable 'foo' !"
   exit
 endif

 print "Hello World !"

 This example creates a standalone program foo from itself.

 See also

 The section about creating a standalone-program, the peek-function and the
 command line options.

 -------------------------------------------------------------------------------

 Name

 box ? draw a rectangle. A synonym for rectangle

 Synopsis

 See the rectangle-command.

 Description

 The box-command does exactly the same as the rectangle-command; it is just a
 synonym. Therefore you should refer to the entry for the rectangle-command for
 further information.

 -------------------------------------------------------------------------------

 Name

 break ? breaks out of one or more loops or switch statements

 Synopsis

 break

 break 2

 Description

 break transfers control immediately outside the enclosing loop or switch
 statement. This is the preferred way of leaving a such a statement (rather than
 goto, which is still possible in most cases). An optional digit allows one to
 break out of multiple levels, e.g. to leave a loop from within a switch
 statement. Please note, that only a literal (e.g. 2) is allowed at this
 location.

 Example

 for a=1 to 10
   break
   print "Hi"
 next a

 while(1)
   break
   print "Hi"
 wend

 repeat
   break
   print "Hi"
 until(0)

 switch 1
 case 1:break
 case 2:case 3:print "Hi"
 end switch

 This example prints nothing at all, because each of the loops (and the
 switch-statement) does an immediate break (before it could print any "Hi").

 See also

 for, while, repeat and switch.

 C

 case ? mark the different cases within a switch-statement
 ceil() ? compute the ceiling for its (float) argument.
 chomp$() ? Remove a single trailing newline from its string-argument; if the
     string does not end in a newline, the string is returned unchanged.
 chr$() ? accepts a number and returns the character at this position within the
     ascii charset
 circle ? draws a circle in the graphic-window
 clear ? Erase circles, rectangles or triangles
 clear screen ? erases the text window
 clear window ? clear the graphic window and begin a new page, if printing is
     under way
 close ? close a file, which has been opened before
 close curve ? close a curve, that has been drawn by the line-command
 close printer ? stops printing of graphics
 close window ? close the graphics-window
 color ? change color for any subsequent drawing-command
 colour ? see color
 compile ? compile a string with yabasic-code on the fly
 continue ? start the next iteration of a for-, do-, repeat- or while-loop
 cos() ? return the cosine of its single argument

 Name

 case ? mark the different cases within a switch-statement

 Synopsis

 switch a
   case 1
   case 2
   ?
 end switch

 ?

 switch a$
   case "a"
   case "b"
   ?
 end switch

 Description

 Please see the switch-statement.

 Example

 input a
 switch(a)
   case 1:print "one":break
   case 2:print "two":break
   default:print "more"
 end switch

 Depending on your input (a number is expected) this code will print one or two
 or otherwise more.

 See also

 switch

 -------------------------------------------------------------------------------

 Name

 ceil() ? compute the ceiling for its (float) argument.

 Synopsis

 print ceil(x)

 Description

 The ceil-function returns the smallest integer number, that is larger or equal
 than its argument.

 Example

 print ceil(1.5),floor(1.5)
 print ceil(2),floor(2)

 Comparing functions ceil and floor, gives a first line of output (1 2), showing
 that ceil is less or equal than floor; but as the second line of output (2 2)
 shows, the two functions give equal results for integer arguments.

 See also

 floor, int, frac

 -------------------------------------------------------------------------------

 Name

 chomp$() ? Remove a single trailing newline from its string-argument; if the
 string does not end in a newline, the string is returned unchanged.

 Synopsis

 print chomp$("Hallo !)

 Description

 The chomp$-function checks, if its string-argument ends in a newline and
 removes it eventually; for this purpose chomp$ can replace an if-statement.
 This can be especially useful, when you deal with input from external sources
 like system$.

 You may apply chomp$ freely, as it only acts, if there is a newline to remove;
 note however, that user-input, that comes from the normal input-statement, does
 not need such a treatment, because it already comes without a newline.

 Example

 The following yabasic-program uses the unix-command whoami to get the username
 of the current user in order to greet him personally. This is done twice: First
 with the chomp$-function and then again with with an equivalent if-statement:

 print "Hello " + chomp$(system$("whoami")) + " !"

 user$ = system$("whoami")
 if (right$(user$,1)=") user$=left$(user$,len(user$)-1)
 print "Hello again " + user$ + " !"

 See also

 system$

 -------------------------------------------------------------------------------

 Name

 chr$() ? accepts a number and returns the character at this position within the
 ascii charset

 Synopsis

 character$=chr$(ascii)

 Description

 The chr$-function is the opposite of the asc-function. It looks up and returns
 the character at the given position within the ascii-charset. It's typical use
 is to construct nonprintable characters which do not occur on your keyboard.

 Nevertheless you won't use chr$ as often as you might think, because the most
 important nonprintable characters can be constructed using escape-sequences
 using the -character (e.g. you might use instead of chr$(10) wherever you
 want to use the newline-character).

 Example

 print "a",chr$(10),"b"

 This will print the letters 'a' and 'b' in different lines because of the
 intervening newline-character, which is returned by chr$(10).

 See also

 asc

 -------------------------------------------------------------------------------

 Name

 circle ? draws a circle in the graphic-window

 Synopsis

 circle x,y,r
 clear circle x,y,r
 fill circle x,y,r
 clear fill circle x,y,r

 Description

 The circle-command accepts three parameters: The x- and y-coordinates of the
 center and the radius of the circle.

 Some more observations related with the circle-command:

   * The graphic-window must have been opened already.

   * The circle may well extend over the boundaries of the window.

   * If you have issued open printer before, the circle will finally appear in
     the printed hard copy of the window.

   * fill circle will draw a filled (with black ink) circle.

   * clear circle will erase (or clear) the outline of the circle.

   * clear fill circle or fill clear circle will erase the full area of the
     circle.

 Example

 open window 200,200

 for n=1 to 2000
   x=ran(200)
   y=ran(200)
   fill circle x,y,10
   clear fill circle x,y,8
 next n

 This code will open a window and draw 2000 overlapping circles within. Each
 circle is drawn in two steps: First it is filled with black ink (fill circle
 x,y,10), then most of this circle is erased again (clear fill circle x,y,8). As
 a result each circle is drawn with an opaque white interior and a 2-pixel
 outline (2-pixel, because the radii differ by two).

 See also

 open window, open printer, line, rectangle, triangle

 -------------------------------------------------------------------------------

 Name

 clear ? Erase circles, rectangles or triangles

 Synopsis

 clear rectangle 10,10,90,90
 clear fill circle 50,50,20
 clear triangle 10,10,20,20,50,30

 Description

 May be used within the circle, rectangle or triangle command and causes these
 shapes to be erased (i.e. be drawn in the colour of the background).

 fill can be used in conjunction with and wherever the fill-clause may appear.
 Used alone, clear will erase the outline (not the interior) of the shape
 (circle, rectangle or triangle); together with fill the whole shape (including
 its interior) is erased.

 Example

 open window 200,200
 fill circle 100,100,50
 clear fill rectangle 10,10,90,90

 This opens a window and draws a pacman-like figure.

 See also

 clear, circle, rectangle, triangle

 -------------------------------------------------------------------------------

 Name

 clear screen ? erases the text window

 Synopsis

 clear screen

 Description

 clear screen erases the text window (the window where the output of print
 appears).

 It must be issued at least once, before some advanced screen-commands (e.g.
 print at or inkey$) may be called; this requirement is due to some limitations
 of the curses-library, which is used by yabasic under Unix for some commands.

 Example

 clear screen
 print "Please press a key : ";
 a$=inkey$
 print a$

 The clear screen command is essential here; if it would be omitted, yabasic
 would issue an error ("need to call 'clear screen' first") while trying to
 execute the inkey$-function.

 See also

 inkey$

 -------------------------------------------------------------------------------

 Name

 clear window ? clear the graphic window and begin a new page, if printing is
 under way

 Synopsis

 clear window

 Description

 clear window clears the graphic window. If you have started printing the
 graphic via open printer, the clear window-command starts a new page as well.

 Example

 open window 200,200
 open printer "t.ps"

 for a=1 to 10
 if (a>1) clear window
 text 100,100,"Hallo "+str$(a)
 next a

 close printer
 close window

 This example prints 10 pages, with the text "Hello 1", "Hello 2", ? and so on.
 The clear screen-command clears the graphics window and starts a new page.

 See also

 open window, open printer

 -------------------------------------------------------------------------------

 Name

 close ? close a file, which has been opened before

 Synopsis

 close filenum
 close # filenum

 Description

 The close-command closes an open file. You should issue this command as soon as
 you are done with reading from or writing to a file.

 Example

 open "my.data" for reading as 1
 input #1 a
 print a
 close 1

 This program opens the file "my.data", reads a number from it, prints this
 number and closes the file again.

 See also

 open

 -------------------------------------------------------------------------------

 Name

 close curve ? close a curve, that has been drawn by the line-command

 Synopsis

 new curve
 line to x1,y1
 ?
 close curve

 Description

 The close curve-command closes a sequence of lines, that has been drawn by
 repeated line to-commands.

 Example

 open window 200,200
 new curve
 line to 100,50
 line to 150,150
 line to 50,150
 close curve

 This example draws a triangle: The three line to-commands draw two lines; the
 final line is however not drawn explicitly, but drawn by the close
 curve-command.

 See also

 line, new curve

 -------------------------------------------------------------------------------

 Name

 close printer ? stops printing of graphics

 Synopsis

 close printer

 Description

 The close printer-command ends the printing graphics. Between open printer and
 close printer everything you draw (e.g. circles, lines ?) is sent to your
 printer. close printer puts an end to printing and will make your printer eject
 the page.

 Example

 open window 200,200
 open printer
 circle 100,100,50
 close printer
 close window

 As soon as close printer is executed, your printer will eject a page with a
 circle on it.

 See also

 open printer

 -------------------------------------------------------------------------------

 Name

 close window ? close the graphics-window

 Synopsis

 close window

 Description

 The close window-command closes the graphics-window, i.e. it makes it disappear
 from your screen. It includes an implicit close printer, if a printer has been
 opened previously.

 Example

 open window 200,200
 circle 100,100,50
 close window

 This example will open a window, draw a circle and close the window again; all
 this without any pause or delay, so the window will be closed before you may
 regard the circle..

 See also

 open window

 -------------------------------------------------------------------------------

 Name

 color ? change color for any subsequent drawing-command

 Synopsis

 colour red,green,blue
 colour "red,green,blue"

 Description

 Change the color, in which lines, dots, circles, rectangles or triangles are
 drawn. The color-command accepts three numbers in the range 0 ? 255 (as in the
 first line of the synopsis above). Those numbers specify the intensity for the
 primary colors red, green and blue respectively. As an example 255,0,0 is red
 and 255,255,0 is yellow.

 Alternatively you may specify the color with a single string (as in the second
 line of the synopsis above); this string should contain three numbers,
 separated by commas. As an example "255,0,255" would be violet. Using this
 variant of the colour-command, you may use symbolic names for colours:

 open window 100,100
 yellow$="255,255,0"
 color yellow$
 text 50,50,"Hallo"

 , which reads much clearer.

 Example

 open window 255,255
 for x=10 to 235 step 10:for y=10 to 235 step 10
         colour x,y,0
         fill rectangle x,y,x+10,y+10
 next y:next x

 This fills the window with colored rectangles. However, none of the used
 colours contains any shade of blue, because the color-command has always 0 as a
 third argument.

 See also

 open window, backcolor, line, rectangle, triangle, circle

 -------------------------------------------------------------------------------

 Name

 colour ? see color

 Synopsis

 colour red,green,blue
 colour "red,green,blue"

 See also

 color

 -------------------------------------------------------------------------------

 Name

 compile ? compile a string with yabasic-code on the fly

 Synopsis

 compile(code$)

 Description

 This is an advanced command (closely related with the execute-command). It
 allows you to compile a string of yabasic-code (which is the only argument).
 Afterwards the compiled code is a normal part of your program.

 Note, that there is no way to remove the compiled code.

 Example

 compile("sub mysub(a):print a:end sub")
 mysub(2)

 This example creates a function named mysub, which simply prints its single
 argument.

 See also

 execute

 -------------------------------------------------------------------------------

 Name

 continue ? start the next iteration of a for-, do-, repeat- or while-loop

 Synopsis

 continue

 Description

 You may use continue within any loop to start the next iteration immediately.
 Depending on the type of the loop, the loop-condition will or will not be
 checked. Especially: for- and while-loops will evaluate their respective
 conditions, do- and repeat-loops will not.

 Remark: Another way to change the flow of execution within a loop, is the
 break-command.

 Example

 for a=1 to 100
   if mod(a,2)=0 continue
   print a
 next a

 This example will print all odd numbers between 1 and 100.

 See also

 for, do, repeat, while, break

 -------------------------------------------------------------------------------

 Name

 cos() ? return the cosine of its single argument

 Synopsis

 x=cos(angle)

 Description

 The cos-function expects an angle (in radians) and returns its cosine.

 Example

 print cos(pi)

 This example will print -1.

 See also

 acos, sin

 D

 data ? introduces a list of data-items
 date$ ? returns a string with various components of the current date
 dec() ? convert a base 2 or base 16 number into decimal form
 default ? mark the default-branch within a switch-statement
 dim ? create an array prior to its first use
 do ? start a (conditionless) do-loop
 doc ? special comment, which might be retrieved by the program itself
 docu$ ? special array, containing the contents of all docu-statement within the
     program
 dot ? draw a dot in the graphic-window

 Name

 data ? introduces a list of data-items

 Synopsis

 data 9,"world"
 ?
 read b,a$

 Description

 The data-keyword introduces a list of comma-separated list of strings or
 numbers, which may be retrieved with the read-command.

 The data-command itself does nothing; it just stores data. A single
 data-command may precede an arbitrarily long list of values, in which strings
 or numbers may be mixed at will.

 yabasic internally uses a data-pointer to keep track of the current location
 within the data-list; this pointer may be reset with the restore-command.

 Example

 do
   restore
   for a=1 to 4
     read num$,num
     print num$,"=",num
   next a
 loop
 data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14

 This example just prints a series of lines eleven=11 up to fourteen=14 and so
 on without end.

 The restore-command ensures that the list of data-items is read from the start
 with every iteration.

 See also

 read, restore

 -------------------------------------------------------------------------------

 Name

 date$ ? returns a string with various components of the current date

 Synopsis

 a$=date$

 Description

 The date$-function (which must be called without parentheses; i.e. date$()
 would be an error) returns a string containing various components of a date; an
 example would be 4-05-27-2004-Thu-May. This string consists of various fields
 separated by hyphens ("-"):

   * The day within the week as a number in the range 0 (=Sunday) to 6 (=
     Saturday) (in the example above: 4, i.e. Thursday).

   * The month as a number in the range 1 (=January) to 12 (=December) (in the
     example: 5 which stands for May).

   * The day within the month as a number in the range 1 to 31 (in the example:
     27).

   * The full, 4-digit year (in the example: 2004, which reminds me that I
     should adjust the clock within my computer ?).

   * The abbreviated name of the day within the week (Mon to Sun).

   * The abbreviated name of the month (Jan to Dec).

 Therefore the whole example above (4-05-27-2004-Thu-May) would read: day 4 in
 the week (counting from 0), May 27 in the year 2004, which is a Thursday in
 May.

 Note, that all fields within the string returned by date$ have a fixed with
 (numbers are padded with zeroes); therefore it is easy to extract the various
 fields of a date format with mid$.

 Example

 rem   Two ways to print the same ...

 print mid$(date$,3,10)

 dim fields$(6)
 a=split(date$,fields$(),"-")
 print fields$(2),"-",fields$(3),"-",fields$(4)

 This example shows two different techniques to extract components from the
 value returned by date$. The mid$-function is the preferred way, but you could
 just as well split the return-value of date$ at every "-" and store the result
 within an array of strings.

 See also

 time$

 -------------------------------------------------------------------------------

 Name

 dec() ? convert a base 2 or base 16 number into decimal form

 Synopsis

 a=dec(number$)
 a=dec(number$,base)

 Description

 The dec-function takes the string-representation of a base-2 or base-16 (which
 is the default) number and converts it into a decimal number. The optional
 second argument (base) might be used to specify a base other than 16. However,
 currently only base 2 or base 16 are supported. Please note, that for base 16
 you may write literals in the usual way, by preceding them with 0x, e.g. like

 print 0xff

 ; this may save you from applying the dec altogether.

 Example

 input "Please enter a binary number: " a$
 print a$," is ",dec(a$)

 See also

 bin$, hex$

 -------------------------------------------------------------------------------

 Name

 default ? mark the default-branch within a switch-statement

 Synopsis

 switch a+3
 case 1
   ?
 case 2
   ?
 default
   ?
 end switch

 Description

 The default-clause is an optional part of the switch-statement (see there for
 more information). It introduces a series of statements, that should be
 executed, if none of the cases matches, that have been specified before (each
 with its own case-clause).

 So default specifies a default to be executed, if none of the explicitly named
 cases matches; hence its name.

 Example

 print "Please enter a number between 0 and 6,"
 print "specifying a day in the week."
 input d
 switch d
 case 0:print "Monday":break
 case 1:print "Tuesday":break
 case 2:print "Wednesday":break
 case 3:print "Thursday":break
 case 4:print "Friday":break
 case 5:print "Saturday":break
 case 6:print "Sunday":break
 default:print "Hey you entered something invalid !"
 end switch

 This program translates a number between 0 and 6 into the name of a weekday;
 the default-case is used to detect (and complain about) invalid input.

 See also

 sub, case

 -------------------------------------------------------------------------------

 Name

 dim ? create an array prior to its first use

 Synopsis

 dim array(x,y)
 dim array$(x,y)

 Description

 The dim-command prepares one or more arrays (of either strings or numbers) for
 later use. This command can also be used to enlarges an existing array.

 When an array is created with the dim-statement, memory is allocated and all
 elements are initialized with either 0 (for numerical arrays) or "" (for string
 arrays).

 If the array already existed, and the dim-statement specifies a larger size
 than the current size, the array is enlarged and any old content is preserved.

 Note, that dim cannot be used to shrink an array: If you specify a size, that
 is smaller than the current size, the dim-command does nothing.

 Finally: To create an array, that is only known within a single subroutine, you
 should use the command local, which creates local variables as well as local
 arrays.

 Example

 dim a(5,5)
 for x=1 to 5:for y=1 to 5
   a(x,y)=int(ran(100))
 next y:next x
 printmatrix(a())
 dim a(7,7)
 printmatrix(a())

 sub printmatrix(ar())
   local x,y,p,q
   x=arraysize(ar(),1)
   y=arraysize(ar(),2)
   for q=1 to y
     for p=1 to y
       print ar(p,q),"	";
     next p
     print
   next q
 end sub

 This example creates a 2-dimensional array (i.e. a matrix) with the
 dim-statement and fills it with random numbers. The second dim-statement
 enlarges the array, all new elements are filled with 0.

 The subroutine printmatrix just does, what its name says.

 See also

 arraysize, arraydim, local

 -------------------------------------------------------------------------------

 Name

 do ? start a (conditionless) do-loop

 Synopsis

 do
 ?
 loop

 Description

 Starts a loop, which is terminated by loop; everything between do and loop will
 be repeated forever. This loop has no condition, so it is an infinite loop;
 note however, that a break- or goto-statement might be used to leave this loop
 anytime.

 Example

 do
   a=a+1
   print a
   if (a>100) break
 loop

 This example prints the numbers between 1 and 101. The break-statement is used
 to leave the loop.

 See also

 loop, repeat, while, break

 -------------------------------------------------------------------------------

 Name

 doc ? special comment, which might be retrieved by the program itself

 Synopsis

 doc   This is a comment
 docu  This is another comment

 Description

 Introduces a comment, which spans up to the end of the line. But other than the
 rem-comment, any docu-comment is collected within the special docu$-array and
 might be retrieved later on. Moreover you might invoke yabasic -docu foo.yab on
 the command line to retrieve the embedded documentation within the program
 foo.yab.

 Instead of doc you may just as well write docu or even documentation.

 Example

 rem   Hi, this has been written by me
 rem
 doc   This program asks for a number and
 doc   prints this number multiplied with 2
 rem
 rem   Print out rhe above message
 for a=1 to arraysize(docu$()):print docu$(a):next a

 rem   Read and print the number
 input "Please input a number: " x
 print x*2

 This program uses the comments within its code to print out a help message for
 the user.

 The contents of the doc-lines are retrieved from the docu$-array; if you do not
 want a comment to be collected within this array, use the rem-statement
 instead.

 See also

 docu$, rem

 -------------------------------------------------------------------------------

 Name

 docu$ ? special array, containing the contents of all docu-statement within the
 program

 Synopsis

 a$=docu$(1)

 Description

 Before your program is executed, yabasic collects the content of all the
 doc-statements within your program within this 1-dimensional array (well only
 those within the main-program, libraries are skipped).

 You may use the arraysize function to find out, how many lines it contains.

 Example

 docu
 docu  This program reads two numbers
 docu  and adds them.
 docu

 rem retrieve and print the embedded documentation
 for a=1 to arraysize(docu$(),1)
   print docu$(a)
 next a

 input "First number: " b
 input "Second number: " c

 print "The sum of ",b," and ",c," is ",b+c

 This program uses the embedded documentation to issue a usage-message.

 See also

 arraydim, rem

 -------------------------------------------------------------------------------

 Name

 dot ? draw a dot in the graphic-window

 Synopsis

 dot x,y
 clear dot x,y

 Description

 Draws a dot at the specified coordinates within your graphic-window. If
 printing is in effect, the dot appears on your printout too.

 Use the functions peek("winheight") or peek("winwidth") to get the size of your
 window and hence the boundaries of the coordinates specified for the
 dot-command.

 Example

 open window 200,200
 circle 100,100,100
 do
   x=ran(200):y=ran(200)
   dot x,y
   total=total+1
   if (sqrt((x-100)^2+(y-100)^2)<100) in=in+1
   print 4*in/total
 loop

 This program uses a well known algorithm to compute ?.

 See also

 line, open window

 E

 else ? mark an alternative within an if-statement
 elsif ? starts an alternate condition within an if-statement
 end ? terminate your program
 endif ? ends an if-statement
 end sub ? ends a subroutine definition
 eof ? check, if an open file contains data
 eor() ? compute the bitwise exclusive or of its two arguments
 error ? raise an error and terminate your program
 euler ? another name for the constant 2.71828182864
 execute$() ? execute a user defined subroutine, which must return a string
 execute() ? execute a user defined subroutine, which must return a number
 exit ? terminate your program
 exp() ? compute the exponential function of its single argument
 export ? mark a function as globally visible

 Name

 else ? mark an alternative within an if-statement

 Synopsis

 if (?) then
   ?
 else
   ?
 endif

 Description

 The else-statement introduces the alternate branch of an if-statement. I.e. it
 starts the sequence of statements, which is executed, if the condition of the
 if-statement is not true.

 Example

 input "Please enter a number: " a
 if (mod(a,2)=1) then
   print a," is odd."
 else
   print a," is even."
 endif

 This program detects, if the number you have entered is even or odd.

 See also

 if

 -------------------------------------------------------------------------------

 Name

 elsif ? starts an alternate condition within an if-statement

 Synopsis

 if (?) then
   ?
 elseif (?)
   ?
 elsif (?) then
   ?
 else
   ?
 endif

 Description

 The elsif-statement is used to select a single alternative among a series of
 choices.

 With each elsif-statement you may specify a condition, which is tested, if the
 main condition (specified with the if-statement) has failed. Note that elsif
 might be just as well written as elseif.

 Within the example below, two variables a and b are tested against a range of
 values. The variable a is tested with the elsif-statement. The very same tests
 are performed for the variable b too; but here an involved series of
 if-else-statements is employed, making the tests much more obscure.

 Example

 input "Please enter a number: " a
 if (a<0) then
   print "less than 0"
 elseif (a<=10) then
   print "between 0 and 10"
 elsif (a<=20)
   print "between 11 and 20"
 else
   print "over 20"
 endif

 input "Please enter another number: " b
 if (b<0) then
   print "less than 0"
 else
   if (b<=10) then
     print "between 0 and 10"
   else
     if (b<=20) then
       print "between 11 and 20"
     else
       print "over 20"
     endif
   endif
 endif

 Note, that the very same tests are performed for the variables a and b, but can
 be stated much more clearly with the elsif-statement.

 Note, that elsif might be written as elseif too, and that the keyword then is
 optional.

 See also

 if, else

 -------------------------------------------------------------------------------

 Name

 end ? terminate your program

 Synopsis

 end

 Description

 Terminate your program. Much (but not exactly) like the exit command.

 Note, that end may not end your program immediately; if you have opened a
 window or called clear screen, yabasic assumes, that your user wants to study
 the output of your program after it has ended; therefore it issues the line
 ---Program done, press RETURN--- and waits for a key to be pressed. If you do
 not like this behaviour, consider using exit.

 Example

 print "Do you want to continue ?"
 input "Please answer y(es) or n(o): " a$
 if (lower$(left$(a$,1))="n") then
   print "bye"
   end
 fi

 See also

 exit

 -------------------------------------------------------------------------------

 Name

 endif ? ends an if-statement

 Synopsis

 if (?) then
   ?
 endif

 Description

 The endif-statement closes (or ends) an if-statement.

 Note, that endif may be written in a variety of other ways: end if, end-if or
 even fi.

 The endif-statement must be omitted, if the if-statement does not contain the
 keyword then (see the example below). Such an if-statement without endif
 extends only over a single line.

 Example

 input "A number please: " a
 if (a<10) then
   print "Your number is less than 10."
 endif

 REM  and now without endif

 input "A number please: " a
 if (a<10) print "Your number is less than 10."

 See also

 if

 -------------------------------------------------------------------------------

 Name

 end sub ? ends a subroutine definition

 Synopsis

 sub foo(?)
   ?
 end sub

 Description

 Marks the end of a subroutine-definition (which starts with the sub-keyword).
 The whole concept of subroutines is explained within the entry for sub.

 Example

 print foo(3)

 sub foo(a)
   return a*2
 end sub

 This program prints out 6. The subroutine foo simply returns twice its
 argument.

 See also

 sub

 -------------------------------------------------------------------------------

 Name

 eof ? check, if an open file contains data

 Synopsis

 open 1,"foo.bar"
 if (eof(1)) then
    ?
 end if

 Description

 The eof-function checks, if there is still data left within an open file. As an
 argument it expects the file-number as returned by (or used within) the
 open-function (or statement).

 Example

 a=open("foo.bar")
 while(not eof(a))
   input #a,a$
   print a$
 end while

 This example will print the contents of the file "foo.bar". The eof-function
 will terminate the loop, if there is no more data left within the file.

 See also

 open

 -------------------------------------------------------------------------------

 Name

 eor() ? compute the bitwise exclusive or of its two arguments

 Synopsis

 print eor(a,b)

 Description

 The eor-function takes two arguments and computes their bitwise exclusive or.
 See your favorite introductory text on informatics for an explanation of this
 function.

 The xor-function is the same as the eor function; both are synonymous; however
 they have each their own description, so you may check out the entry of xor for
 a slightly different view.

 Example

 for a=0 to 3
   for b=0 to 3
     print fill$(bin$(a))," eor ",fill$(bin$(b))," = ",fill$(bin$(eor(a,b)))
   next b
 next a

 sub fill$(a$)
   return right$("0"+a$,2)
 end sub

 This example prints a table, from which you may figure, how the eor-function is
 computed.

 See also

 and, or

 -------------------------------------------------------------------------------

 Name

 error ? raise an error and terminate your program

 Synopsis

 error "Wrong, wrong, wrong !!"

 Description

 Produces the same kind or error messages, that yabasic itself produces (e.g. in
 case of a syntax-error). The single argument is issued along with the current
 line-number.

 Example

 input "Please enter a number between 1 and 10: " a
 if (a<1 or a>10) error "Oh no ..."

 This program is very harsh in checking the users input; instead of just asking
 again, the program terminates with an error, if the user enters something
 wrong.

 The error message would look like this:

 ---Error in t.yab, line 2: Oh no ...
 ---Error: Program stopped due to an error

 See also

 Well, there should be a corresponding called warning; unfortunately ther is
 none yet.

 -------------------------------------------------------------------------------

 Name

 euler ? another name for the constant 2.71828182864

 Synopsis

 foo=euler

 Description

 euler is the well known constant named after Leonard Euler; its value is
 2.71828182864. euler is not a function, so parens are not allowed (i.e. euler()
 will produce an error). Finally, you may not assign to euler; it wouldn't sense
 anyway, because it is a constant.

 Example

 print euler

 See also

 pi

 -------------------------------------------------------------------------------

 Name

 execute$() ? execute a user defined subroutine, which must return a string

 Synopsis

 print execute$("foo$","arg1","arg2")

 Description

 execute$ can be used to execute a user defined subroutine, whose name may be
 specified as a string expression.

 This feature is the only way to execute a subroutine, whose name is not known
 by the time you write your program. This might happen, if you want to execute a
 subroutine, which is compiled (using the compile command) during the course of
 execution of your program.

 Note however, that the execute$-function is not the preferred method to execute
 a user defined subroutine; in almost all cases you should just execute a
 subroutine by writing down its name within your yabasic program (see the
 example).

 Example

 print execute$("foo$","Hello","world !")
 sub foo$(a$,b$)
   return a$+" "+b$
 end sub

 The example simply prints Hello world !, which is the return value of the user
 defined subroutine foo$. The same could be achieved by executing:

 print foo$(a$,b$)

 See also

 compile, execute

 -------------------------------------------------------------------------------

 Name

 execute() ? execute a user defined subroutine, which must return a number

 Synopsis

 print execute("bar","arg1","arg2")

 Description

 The execute-function is the counterpart of the execute$-function (please see
 there for some caveats). execute executes subroutines, which returns a number.

 Example

 print execute("bar",2,3)
 sub bar(a,b)
   return a+b
 end sub

 See also

 compile, execute$

 -------------------------------------------------------------------------------

 Name

 exit ? terminate your program

 Synopsis

 exit
 exit 1

 Description

 Terminate your program and return any given value to the operating system. exit
 is similar to end, but it will terminate your program immediately, no matter
 what.

 Example

 print "Do you want to continue ?"
 input "Please answer y(es) or n(o): " a$
 if (lower$(left$(a$,1))="n") exit 1

 See also

 end

 -------------------------------------------------------------------------------

 Name

 exp() ? compute the exponential function of its single argument

 Synopsis

 foo=exp(bar)

 Description

 This function computes e to the power of its argument, where e is the well
 known euler constant 2.71828182864.

 The exp-function is the inverse of the log-function.

 Example

 open window 100,100
 for x=0 to 100
    dot x,100-100*exp(x/100)/euler
 next x

 This program plots part of the exp-function, however the range is rather small,
 so that you may not recognize the function from this plot.

 See also

 log

 -------------------------------------------------------------------------------

 Name

 export ? mark a function as globally visible

 Synopsis

 export sub foo(bar)
 ?
 end sub

 Description

 The export-statement is used within libraries to mark a user defined subroutine
 as visible outside the library wherein it is defined. Subroutines, which are
 not exported, must be qualified with the name of the library, e.g. foo.baz
 (where foo is the name of the library and baz the name of the subroutine);
 exported subroutines may be used without specifying the name of the library,
 e.g. bar.

 Therefore export may only be useful within libraries.

 Example

 The library foo.bar (which is listed below) defines two functions bar and baz,
 however only the function bar is exported and therefore visible even outside
 the library; baz is not exported and may only be used within the library
 foo.yab:

 export sub bar()
   print "Hello"
 end sub

 sub baz()
   print "World"
 end sub

 Now within your main program cux.yab (which imports the library foo.yab); note
 that this program produces an error:

 import foo

 print "Calling subroutine foo.bar (okay) ..."
 foo.bar()
 print "done."

 print "Calling subroutine bar (okay) ..."
 bar()
 print "done."

 print "Calling subroutine foo.baz (okay) ..."
 foo.baz()
 print "done."

 print "Calling subroutine baz (NOT okay) ..."
 baz()
 print "done."

 The output when executing yabasic foo.yab is this:

 Calling subroutine foo.bar (okay) ...
 Hello
 done.
 Calling subroutine bar (okay) ...
 Hello
 done.
 Calling subroutine foo.baz (okay) ...
 World
 done.
 Calling subroutine baz (NOT okay) ...
 ---Error in main.yab, line 16: can't find subroutine 'baz'
 ---Dump: sub baz() called in main.yab,16
 ---Error: Program stopped due to an error

 As the error message above shows, the subroutine baz must be qualified with the
 name of the library, if used outside the library, wherein it is defined (e.g.
 foo.baz. I.e. outside the library foo.yab you need to write foo.baz. baz alone
 would be an error.

 The subroutine bar (without adding the name of the library) however may (and
 probably should) be used in any program, which imports the library foo.yab.

 Note

 In some sense the set of exported subroutines constitutes the interface of a
 library.

 See also

 sub, import

 F

 false ? a constant with the value of 0
 fi ? another name for endif
 fill ? draw a filled circles, rectangles or triangles
 floor() ? compute the floor for its (float) argument.
 for ? starts a for-loop
 frac() ? return the fractional part of its numeric argument

 Name

 false ? a constant with the value of 0

 Synopsis

 okay=false

 Description

 The constant false can be assigned to variables which later appear in
 conditions (e.g. within an if-statement.

 false may also be written as FALSE or even FaLsE.

 Example

 input "Please enter a number between 1 and 10: " a
 if (check_input(a)) print "Okay"

 sub check_input(x)
   if (x>10 or x<1) return false
   return true
 end sub

 The subroutine check_input checks its argument and returns true or false
 according to the outcome of the check..

 See also

 true

 -------------------------------------------------------------------------------

 Name

 fi ? another name for endif

 Synopsis

 if (?)
 ?
 fi

 Description

 fi marks the end of an if-statement and is exactly equivalent to endif, please
 see there for further information.

 Example

 input "A number please: " a
 if (a<10) then
   print "Your number is less than 10."
 fi

 See also

 endif

 -------------------------------------------------------------------------------

 Name

 fill ? draw a filled circles, rectangles or triangles

 Synopsis

 fill rectangle 10,10,90,90
 fill circle 50,50,20
 fill triangle 10,20,20,10,20,20

 Description

 The keyword fill may be used within the circle, rectangle or triangle command
 and causes these shapes to be filled.

 fill can be used in conjunction with and wherever the clear-clause may appear.
 Used alone, fill will fill the interior of the shape (circle, rectangle or
 triangle); together with clear the whole shape (including its interior) is
 erased.

 Example

 open window 200,200
 fill circle 100,100,50
 clear fill rectangle 10,10,90,90

 This opens a window and draws a pacman-like figure.

 See also

 clear, circle, rectangle, triangle

 -------------------------------------------------------------------------------

 Name

 floor() ? compute the floor for its (float) argument.

 Synopsis

 print floor(x)

 Description

 The floor-function returns the largest integer number, that is smaller or equal
 than its argument. For positive numbers x, floor(x) is the same as int(x); for
 negaive numbers it can be different (see the example below).

 Example

 print int(-1.5),floor(-1.5)
 print int(-1),floor(-1)
 print int(1.5),floor(1.5)

 This example compares the functions int and floor, starting with -1 -2, then -1
 -1 and ending with 1 1, which shows the different behaviour of both functions.

 See also

 ceil, int, frac

 -------------------------------------------------------------------------------

 Name

 for ? starts a for-loop

 Synopsis

 for a=1 to 100 step 2
   ?
 next a

 Description

 The for-loop lets its numerical variable (a in the synopsis) assume all values
 within the given range. The optional step-clause may specify a value (default:
 1) by which the variable will be incremented (or decremented, if step is
 negative).

 Any for-statement can be replaced by a set of ifs and gotos; as you may infer
 from the example below this is normally not feasible. However if you want to
 know in detail how the for-statement works, you should study this example,
 which presents a for-statement and an exactly equivalent series of ifs and
 gotos.

 Example

 for a=1 to 10 step 2:print a:next

 a=1
 label check
 if (a>10) goto done
   print a
   a=a+2
 goto check
 label done

 This example simply prints the numbers 1, 3, 5, 7 and 9. It does this twice:
 First with a simple for-statement and then with ifs and gotos.

 See also

 step, next

 -------------------------------------------------------------------------------

 Name

 frac() ? return the fractional part of its numeric argument

 Synopsis

 x=frac(y)

 Description

 The frac-function takes its argument, removes all the digits to the left of the
 comma and just returns the digits right of the comma, i.e. the fractional part.

 Refer to the example to learn how to rewrite frac by employing the int-function
 (which is not suggested anyway).

 Example

 for a=1 to 10
   print frac(sqr(a))
   print sqr(a)-int(sqr(a))
 next a

 The example prints the fractional part of the square root of the numbers
 between 1 and 10. Each result is computed (and printed) twice: Once by
 employing the frac-function and once by employing the int-function.

 See also

 int, floor, ceil

 G

 getbit$() ? return a string representing the bit pattern of a rectangle within
     the graphic window
 getscreen$() ? returns a string representing a rectangular section of the text
     terminal
 glob() ? check if a string matches a simple pattern
 gosub ? continue execution at another point within your program (and return
     later)
 goto ? continue execution at another point within your program (and never come
     back)

 Name

 getbit$() ? return a string representing the bit pattern of a rectangle within
 the graphic window

 Synopsis

 a$=getbit$(10,10,20,20)
 a$=getbit$(10,10 to 20,20)

 Description

 The function getbit returns a string, which contains the encoded bit-pattern of
 a rectangle within graphic window; the four arguments specify two opposite
 corners of the rectangle. The string returned might later be fed to the putbit
 -command.

 The getbit$-function might be used for simple animations (as in the example
 below).

 Example

 open window 40,40
 fill circle 20,20,18
 circle$=getbit$(0,0,40,40)
 close window

 open window 200,200
 for x=1 to 200
   putbit circle$,x,80
 next x

 This example features a circle moving from left to right over the window.

 See also

 putbit

 -------------------------------------------------------------------------------

 Name

 getscreen$() ? returns a string representing a rectangular section of the text
 terminal

 Synopsis

 a$=getscreen$(2,2,20,20)

 Description

 The getscreen$ function returns a string representing the area of the screen as
 specified by its four arguments (which specify two opposite corners). I.e.
 everything you have printed within this rectangle will be encoded in the string
 returned (including any colour-information).

 Like most other commands dealing with advanced text output, getscreen$
 requires, that you have called clear screen before.

 Example

 clear screen

 for a=1 to 1000:
         print color("red") "1";
         print color("green") "2";
         print color("blue") "3";
 next a
 screen$=getscreen$(10,10,40,10)
 print at(10,10) " Please Press 'y' or 'n' ! "
 a$=inkey$
 putscreen screen$,10,10

 This program fills the screen with colored digits and afterwards asks the user
 for a choice ( Please press 'y' or 'n' ! ). Afterwards the area of the screen,
 which has been overwritten by the question will be restored with its previous
 contents, whhch had been saved via getscreen$.

 See also

 putscreen$

 -------------------------------------------------------------------------------

 Name

 glob() ? check if a string matches a simple pattern

 Synopsis

 if (glob(string$,pattern$)) ?

 Description

 The glob-function takes two arguments, a string and a (glob-) pattern, and
 checks if the string matches the pattern. However glob does not employ the
 powerful rules of regular expressions; rather it has only two special
 characters: * (which matches any number (even zero) of characters) and ? (which
 matches exactly a single character).

 Example

 for a=1 to 10
   read string$,pattern$
   if (glob(string$,pattern$)) then
     print string$," matches ",pattern$
   else
     print string$," does not match ",pattern$
   endif
 next a

 data "abc","a*"
 data "abc","a?"
 data "abc","a??"
 data "abc","*b*"
 data "abc","*"
 data "abc","???"
 data "abc","?"
 data "abc","*c"
 data "abc","A*"
 data "abc","????"

 This program checks the string abc against various patterns and prints the
 result. The output is:

 abc matches a*
 abc does not match a?
 abc matches a??
 abc matches *b*
 abc matches *
 abc matches ???
 abc does not match ?
 abc matches *c
 abc does not match A*
 abc does not match ????

 See also

 There are no related commands.

 -------------------------------------------------------------------------------

 Name

 gosub ? continue execution at another point within your program (and return
 later)

 Synopsis

 gosub foo

 ?

 label foo
 ?
 return

 Description

 gosub remembers the current position within your program and then passes the
 flow of execution to another point (which is normally marked with a label).
 Later, when a return-statement is encountered, the execution is resumed at the
 previous location.

 gosub is the traditional command for calling code, which needs to be executed
 from various places within your program. However, with subroutines yabasic
 offers a much more flexible way to achieve this (and more). Therefore gosub
 must to be considered obsolete.

 Example

 print "Do you want to exit ? "
 gosub ask
 if (r$="y") exit

 label ask
 input "Please answer yes or no, by typing 'y' or 'n': ",r$
 return

 See also

 return, goto, sub, label, on gosub

 -------------------------------------------------------------------------------

 Name

 goto ? continue execution at another point within your program (and never come
 back)

 Synopsis

 goto foo

 ?

 label foo

 Description

 The goto-statement passes the flow of execution to another point within your
 program (which is normally marked with a label).

 goto is normally considered obsolete and harmful, however in yabasic it may be
 put to the good use of leaving loops (e.g. while or for) prematurely. Note
 however, that subroutines may not be left with the goto-statement.

 Example

 print "Please press any key to continue."
 print "(program will continue by itself within 10 seconds)"
 for a=1 to 10
   if (inkey$(1)<>"") then goto done
 next a
 label done
 print "Hello World !"

 Here the goto-statement is used to leave the for-loop prematurely.

 See also

 gosub, on goto

 H

 hex$() ? convert a number into hexadecimal

 Name

 hex$() ? convert a number into hexadecimal

 Synopsis

 print hex$(foo)

 Description

 The hex$-function converts a number into a string with its hexadecimal
 representation. hex$ is the inverse of the dec-function.

 Example

 open 1,"foo"
 while(!eof(1))
   print right$("0"+hex$(peek(1)),2)," ";
   i=i+1
   if (mod(i,10)=0) print
 end while
 print

 This program reads the file foo and prints its output as a hex-dump using the
 hex-function.

 See also

 decbin

 I

 if ? evaluate a condition and execute statements or not, depending on the
     result
 import ? import a library
 inkey$ ? wait, until a key is pressed
 input ? read input from the user (or from a file) and assign it to a variable
 instr() ? searches its second argument within the first; returns its position
     if found
 int() ? return the integer part of its single numeric argument

 Name

 if ? evaluate a condition and execute statements or not, depending on the
 result

 Synopsis

 if (?) then
   ?
 endif

 if (?) ?

 if (?) then
   ?
 else
   ?
 endif

 if (?) then
   ?
 elsif (?)
   ?
 elsif (?) then
   ?
 else
   ?
 endif

 Description

 The if-statement is used to evaluate a conditions and take actions accordingly.
 (As an aside, please note that there is no real difference between conditions
 and expressions.)

 There are two major forms of the if-statement:

   * The one-line-form without the keyword then:

     if (?) ?

     This form evaluates the condition and if the result is true executes all
     commands (separated by colons) upt to the end of the line. There is neither
     an endif keyword nor an else-branch.

   * The multi-line-form with the keyword then:

     if (?) then ? elsif (?) ? else ? endif

     (where elsif and else are optional, whereas endif is not.

     According to the requirements of your program, you may specify:

       + elsif(?), which specifies a condition, that will be evaluated only if
         the condition(s) within if or any preceding elsif did not match.

       + else, which introduces a sequence of commands, that will be executed,
         if none of the conditions above did match.

       + endif is required and ends the if-statement.

 Example

 input "Please enter a number between 1 and 4: " a
 if (a<=1 or a>=4) error "Wrong, wrong !"
 if (a=1) then
   print "one"
 elsif (a=2)
   print "two"
 elsif (a=3)
   print "three"
 else
   print "four"
 endif

 The input-number between 1 and 4 is simply echoed as text (one, two, ?). The
 example demonstrates both forms (short and long) of the if-statement (Note
 however, that the same thing can be done, probably somewhat more elegant, with
 the switch-statement).

 See also

 else, elsif, endif, conditions and expressions.

 -------------------------------------------------------------------------------

 Name

 import ? import a library

 Synopsis

 import foo

 Description

 The import-statement imports a library. It expects a single argument, which
 must be the name of a library (without the trailing .yab). This library will
 then be read and parsed and its subroutines (and variables) will be made
 available within the importing program. Most of the time this will be the main
 program, but libraries my also import and use other libraries.

 Libraries will first be searched in three locations in order:

   * The current directory, i.e. the directory from which you have invoked
     yabasic)

   * The directory, where your main program lives. This can be different from
     the first directory, if you specify a path for your main program, e.g. like
     yabasic foo/bar.yab.

   * Finally, libraries are searched within a special directory, whose exact
     location depends on your system or options when invoking yabasic. Typical
     values would be /usr/lib under Unix or C:yabasicndows.
     Invoking yabasic --help will show the correct directory. The location of
     this directory may be changed with the option --librarypath (see options).

 Example

 Lets say you have a yabasic-program foo.yab, which imports a library lib.yab.
 foo.yab; this would read:

 import lib

 rem  This works
 lib.x(0)

 rem  This works too
 x(1)

 rem  And this
 lib.y(2)

 rem  But this not !
 y(3)

 Now the library lib.yab reads:

 rem  Make the subroutine x easily available outside this library
 export sub x(a)
   print a
   return
 end sub

 rem  sub y must be referenced by its full name
 rem  outside this library
 sub y(a)
   print a
   return
 end sub

 This program produces an error:

 0
 1
 2
 ---Error in foo.yab, line 13: can't find subroutine 'y'
 ---Dump: sub y() called in foo.yab,13
 ---Error: Program stopped due to an error

 As you may see from the error message, yabasic is unable to find the subroutine
 y without specifying the name of the library (i.e. lib.y). The reason for this
 is, that y, other than x, is not exported from the library lib.yab (using the
 export-statement).

 See also

 export, sub

 -------------------------------------------------------------------------------

 Name

 inkey$ ? wait, until a key is pressed

 Synopsis

 clear screen
 foo$=inkey$
 inkey$
 foo$=inkey$(bar)
 inkey$(bar)

 Description

 The inkeys$-function waits, until the user presses a key on the keyboard or a
 button of his mouse, and returns this very key. An optional argument specifies
 the number of seconds to wait; if omitted, inkey$ will wait indefinitely.

 inkey$ may only be used, if clear screen has been called at least once.

 For normal keys, yabasic simply returns the key, e.g. a, 1 or !. For function
 keys you will get f1, f2 and so on. Other special keys will return these
 strings respectively: enter, backspace, del, esc, scrnup (for screen up),
 scrndown and tab. Modifier keys (e.g. ctrl, alt or shift) by themselves can not
 be detected (e.g. if you simultaneously press shift and 'a', inkey$ will return
 the letter 'A' instead of 'a' of course).

 If a graphical window has been opened (via open window) any mouseclick within
 this window will be returned by inkey$ too. The string returned (e.g.
 MB1d+0:0028,0061, MB2u+0:0028,0061 or MB1d+1:0028,0061) is constructed as
 follows:

   * Every string associated with a mouseclick will start with the fixed string
     MB

   * The next digit (1, 2 or 3) specifies the mousebutton pressed.

   * A single letter, d or u, specifies, if the mousebutton has been pressed or
     released: d stands for down, i.e. the mousebutton has been pressed; u means
     up, i.e. the mousebutton has been released.

   * The plus-sign ('+'), which follows is always fixed.

   * The next digit (in the range 0 to 7) encodes the modifier keys pressed,
     where 1 stands for shift, 2 stands for alt and 4 stands for ctrl.

   * The next four digits (e.g. 0028) contain the x-position, where the
     mousebutton has been pressed.

   * The comma to follow is always fixed.

   * The last four digits (e.g. 0061) contain the y-position, where the
     mousebutton has been pressed.

 All those fields are of fixed length, so you may use functions like mid$ to
 extract certain fields. However, note that with mousex, mousey, mouseb and
 mousemod there are specialized functions to return detailed information about
 the mouseclick. Finally it should be noted, that inkey$ will only register
 mouseclicks within the graphic-window; mouseclicks in the text-window cannot be
 detected.

 inkey$ accepts an optional argument, specifying a timeout in seconds; if no key
 has been pressed within this span of time, an empty string is returned. If the
 timeout-argument is omitted, inkey$ will wait for ever.

 Example

 clear screen
 open window 100,100
 print "Press any key or press 'q' to stop."
 repeat
   a$=inkey$
   print a$
 until(a$="q")

 This program simply returns the key pressed. You may use it, to learn, which
 strings are returned for the special keys on your keyboard (e.g.
 function-keys).

 See also

 clear screen,mousex, mousey, mouseb, mousemod

 -------------------------------------------------------------------------------

 Name

 input ? read input from the user (or from a file) and assign it to a variable

 Synopsis

 input a
 input a,b,c
 input a$
 input "Hello" a
 input #1 a$

 Description

 input reads the new contents of one or many (numeric- or string-) variables,
 either from the keyboard (i.e. from you) or from a file. An optional first
 string-argument specifies a prompt, which will be issued before reading any
 contents.

 If you want to read from an open file, you need to specify a hash ('#'),
 followed by the number, under which the file has been opened.

 Note, that the input is split at spaces, i.e. if you enter a whole line
 consisting of many space-separated word, the first input-statement will only
 return the first word; the other words will only be returned on subsequent
 calls to input; the same applies, if a single input reads multiple variables:
 The first variable gets only the first word, the second one the second word,
 and so on. If you don't like this behaviour, you may use line input, which
 returns a whole line (including embedded spaces) at once.

 Example

 input "Please enter the name of a file to read: " a$
 open 1,a$
 while(!eof(1))
   input #1 b$
   print b$
 wend

 If this program is stored within a file test.yab and you enter this name when
 prompted for a file to read, you will see this output:

 Please enter the name of a file to read: t.yab
 input
 "Please
 enter
 the
 name
 of
 a
 file
 to
 read:
 "
 a$
 open
 1,a$
 while(!eof(1))
 input
 #1
 b$
 print
 b$
 wend

 See also

 line input

 -------------------------------------------------------------------------------

 Name

 instr() ? searches its second argument within the first; returns its position
 if found

 Synopsis

 print instr(a$,b$)
 if (instr(a$,b$)) ?
 pos=instr(a$,b$,x)

 Description

 The instr-functions requires two string arguments and searches the second
 argument within the first. If the second argument can be found within the
 first, the position is returned (counting from one). If it can not be found,
 the instr-function returns 0; this makes this function usable within the
 condition of an if-statement (see the example below).

 If you supply a third, numeric argument to the instr-function, it will be used
 as a starting point for the search. Therefore instr("abcdeabcdeabcde","e",8)
 will return 10, because the search for an "e" starts at position 8 and finds
 the "e" at position 10 (and not the one at position 5).

 Example

 input "Please enter a text containing the string 'cat': " a$
 if (instr(a$,"cat")) then
   print "Well done !"
 else
   print "No cat in your input ..."
 endif

 See also

 rinstr

 -------------------------------------------------------------------------------

 Name

 int() ? return the integer part of its single numeric argument

 Synopsis

 print int(a)

 Description

 The int-function returns only the digits before the comma; int(2.5) returns 2
 and int(-2.3) returns -2.

 Example

 input "Please enter a whole number between 1 and 10: " a
 if (a=int(a) and a>=1 and a<=10) then
   print "Thanx !"
 else
   print "Never mind ..."
 endif

 See also

 frac, floor, ceil

 L

 label ? mark a specific location within your program for goto, gosub or restore
 left$() ? return (or change) left end of a string
 len() ? return the length of a string
 line ? draw a line
 line input ? read in a whole line of text and assign it to a variable
 local ? mark a variable as local to a subroutine
 log() ? compute the natural logarithm
 loop ? marks the end of an infinite loop
 lower$() ? convert a string to lower case
 ltrim$() ? trim spaces at the left end of a string

 Name

 label ? mark a specific location within your program for goto, gosub or restore

 Synopsis

 label foo

 ?

 goto foo

 Description

 The label-command can be used to give a name to a specific location within your
 program. Such a position might be referred from one of three commands: goto,
 gosub and restore.

 You may use labels safely within libraries, because a label (e.g. foo) does not
 collide with a label with the same name within the main program or within
 another library; yabasic will not mix them up.

 As an aside, please note, that line numbers are a special (however deprecated)
 case of labels; see the second example below.

 Example

 for a=1 to 100
   if (ran(10)>5) goto done
 next a
 label done

 10 for a=1 to 100
 20   if (ran(10)>5) goto 40
 30 next a
 40

 Within this example, the for-loop will probably be left prematurely with a
 goto-statement. This task is done twice: First with labels and then again with
 line numbers.

 See also

 gosub, goto.

 -------------------------------------------------------------------------------

 Name

 left$() ? return (or change) left end of a string

 Synopsis

 print left$(a$,2)
 left$(b$,3)="foobar"

 Description

 The left$-function accepts two arguments (a string and a number) and returns
 the part from the left end of the string, whose length is specified by its
 second argument. Loosely spoken, it simply returns the requested number of
 chars from the left end of the given string.

 Note, that the left$-function can be assigned to, i.e. it may appear on the
 left hand side of an assignment. In this way it is possible to change a part of
 the variable used within the left$-function. Note, that that way the length of
 the string cannot be changed, i.e. characters might be overwritten, but not
 added. For an example see below.

 Example

 input "Please answer yes or no: " a$
 l=len(a$):a$=lower$(a$):print "Your answer is ";
 if (left$("yes",l)=a$ and l>=1) then
   print "yes"
 elsif (left$("no",l)=a$ and l>=1) then
   print "no"
 else
   print "?"
 endif

 This example asks a simple yes/no question and goes some way to accept even
 incomplete input, while still being able to reject invalid input.

 This second example demonstrates the capability to assign to the
 left$-function.

 a$="Heiho World !"
 print a$
 left$(a$,5)="Hello"
 print a$

 See also

 right$, mid$

 -------------------------------------------------------------------------------

 Name

 len() ? return the length of a string

 Synopsis

 x=len(a$)

 Description

 The len-function returns the length of its single string argument.

 Example

 input "Please enter a password: " a$
 if (len(a$)<6) error "Password too short !"

 This example checks the length of the password, that the user has entered.

 See also

 left$, right$ and mid$,

 -------------------------------------------------------------------------------

 Name

 line ? draw a line

 Synopsis

 open window 100,100
 line 0,0,100,100
 line 0,0 to 100,100
 new curve
 line 100,100
 line to 100,100

 open window 100,100
 clear line 0,0,100,100
 clear line 0,0 to 100,100
 new curve
 clear line 100,100
 clear line to 100,100

 Description

 The line-command draws a line. Simple as this is, the line-command has a large
 variety of forms as they are listed in the synopsis above. Lets look at them a
 little closer:

   * A line has a starting and an end point; therefore the line-command
     (normally) needs four numbers as arguments, representing these two points.
     This is the first form appearing within the synopsis.

   * You may separate the two points with either ',' or to, which accounts for
     the second form of the line-command.

   * The line-command may be used to draw a connected sequence of lines with a
     sequence of commands like line x,y; Each command will draw a line from the
     point where the last line-command left off, to the point specified in the
     arguments. Note, that you need to use the command new curve before you may
     issue such a line-command. See the example below.

   * You may insert the word to for beauty: line to x,y, which does exactly the
     same as line x,y

   * Finally, you may choose not to draw, but to erase the lines; this can be
     done by prepending the phrase clear. This account for all the other forms
     of the line-command.

 Example

 open window 200,200
 line 10,10 to 10,190
 line 10,190 to 190,190
 new curve
 for a=0 to 360
   line to 10+a*180/360,100+60*sin(a*pi/180)
 next a

 This example draws a sine-curve (with an offset in x- and y-direction). Note,
 that the first line-command after new curve does not draw anything. Only the
 coordinates will be stored. The second iteration of the loop then uses these
 coordinates as a starting point for the first line.

 See also

 new curve, close curve, open window

 -------------------------------------------------------------------------------

 Name

 line input ? read in a whole line of text and assign it to a variable

 Synopsis

 line input a
 line input a$
 line input "Hello" a
 line input #1 a$

 Description

 In most respects line input is like the input-command: It reads the new
 contents of a variable, either from keyboard or from a file. However, line
 input always reads a complete line and assigns it to its variable. line input
 does not stop reading at spaces and is therefore the best way to read in a
 string which might contain whitespace. Note, that the final newline is stripped
 of.

 Example

 line input "Please enter your name (e.g. Frodo Beutelin): " a$
 print "Hello ",a$

 Note that the usage of line input is essential in this example; a simple
 input-statement would only return the string up to the first space, e.g. Frodo.

 See also

 input

 -------------------------------------------------------------------------------

 Name

 local ? mark a variable as local to a subroutine

 Synopsis

 sub foo()

   local a,b,c$,d(10),e$(5,5)

   ?

 end sub

 Description

 The local-command can (and should be) used to mark a variable (or array) as
 local to the containing subroutine. This means, that a local variable in your
 subroutine is totally different from a variable with the same name within your
 main program. Variables which are known everywhere within your program are
 called global in contrast.

 Declaring variables within the subroutine as local helps to avoid hard to find
 bugs; therefore local variables should be used whenever possible.

 Note, that the parameters of your subroutines are always local.

 As you may see from the example, local arrays may be created without using the
 keyword dim (which is required only for global arrays).

 Example

 a=1
 b=1
 print a,b
 foo()
 print a,b

 sub foo()
   local a
   a=2
   b=2
 end sub

 This example demonstrates the difference between local and global variables; it
 produces this output:

 1 1
 1 2

 As you may see, the content of the global variable a is unchanged after the
 subroutine foo; this is because the assignment a=2 within the subroutine
 affects the local variable a only and not the global one. However, the variable
 b is never declared local and therefore the subroutine changes the global
 variable, which is reflected in the output of the second print-statement.

 See also

 sub, static, dim

 -------------------------------------------------------------------------------

 Name

 log() ? compute the natural logarithm

 Synopsis

 a=log(x)
 a=log(x,base)

 Description

 The log-function computes the logarithm of its first argument. The optional
 second argument gives the base for the logarithm; if this second argument is
 omitted, the euler-constant 2.71828? will be taken as the base.

 Example

 open window 200,200
 for x=10 to 190 step 10:for y=10 to 190 step 10
   r=3*log(1+x,1+y)
   if (r>10) r=10
   if (r<1) r=1
   fill circle x,y,r
 next y:next x

 This draws another nice plot.

 See also

 exp

 -------------------------------------------------------------------------------

 Name

 loop ? marks the end of an infinite loop

 Synopsis

 do
   ?
 loop

 Description

 The loop-command marks the ends of a loop (which is started by do), wherein all
 statements within the loop are repeated forever. In this respect the do
 loop-loop is infinite, however, you may leave it anytime via break or goto.

 Example

 print "Hello, I will throw dice, until I get a 2 ..."
 do
   r=int(ran(6))+1
   print r
   if (r=2) break
 loop

 See also

 do, for, repeat, while, break

 -------------------------------------------------------------------------------

 Name

 lower$() ? convert a string to lower case

 Synopsis

 l$=lower$(a$)

 Description

 The lower$-function accepts a single string-argument and converts it to all
 lower case.

 Example

 input "Please enter a password: " a$
 if (a$=lower$(a$)) error "Your password is NOT mixed case !"

 This example prompts for a password and checks, if it is really lower case.

 See also

 upper$

 -------------------------------------------------------------------------------

 Name

 ltrim$() ? trim spaces at the left end of a string

 Synopsis

 a$=ltrim$(b$)

 Description

 The ltrim$-function removes all whitespace from the left end of a string and
 returns the result.

 Example

 input "Please answer 'yes' or 'no' : " a$
 a$=lower$(ltrim$(rtrim$(a$)))
 if (len(a$)>0 and a$=left$("yes",len(a$))) then
   print "Yes ..."
 else
   print "No ..."
 endif

 This example prompts for an answer and removes any spaces, which might precede
 the input; therefore it is even prepared for the (albeit somewhat pathological
 case, that the user first hits space before entering his answer.

 See also

 rtrim$, trim$

 M

 max() ? return the larger of its two arguments
 mid$() ? return (or change) characters from within a string
 min() ? return the smaller of its two arguments
 mod ? compute the remainder of a division
 mouseb ? extract the state of the mousebuttons from a string returned by inkey$
 mousemod ? return the state of the modifier keys during a mouseclick
 mousex ? return the x-position of a mouseclick
 mousey ? return the y-position of a mouseclick

 Name

 max() ? return the larger of its two arguments

 Synopsis

 print max(a,b)

 Description

 Return the maximum of its two arguments.

 Example

 dim m(10)
 for a=1 to 1000
   m=0
   For b=1 to 10
     m=max(m,ran(10))
   next b
   m(m)=m(m)+1
 next a

 for a=1 to 9
   print a,": ",m(a)
 next a

 Within the inner for-loop (the one with the loop-variable b), the example
 computes the maximum of 10 random numbers. The outer loop (with the loop
 variable a) now repeats this process 1000 times and counts, how often each
 maximum appears. The last loop finally reports the result.

 Now, the interesting question would be, which will be approached, when we
 increase the number of iterations from thousand to infinity. Well, maybe
 someone could just tell me :-)

 See also

 min

 -------------------------------------------------------------------------------

 Name

 mid$() ? return (or change) characters from within a string

 Synopsis

 print mid$(a$,2,1)
 print mid$(a$,2)
 mid$(a$,5,3)="foo"
 mid$(a$,5)="foo"

 Description

 The mid$-function requires three arguments: a string and two numbers, where the
 first number specifies a position within the string and the second one gives
 the number of characters to be returned; if you omit the second argument, the
 mid$-function returns all characters up to the end of the string.

 Note, that you may assign to the mid$-function, i.e. mid$ may appear on the
 left hand side of an assignment. In this way it is possible to change a part of
 the variable used within the mid$-function. Note, that that way the length of
 the string cannot be changed, i.e. characters might be overwritten, but not
 added. For an example see below.

 Example

 input "Please enter a string: " a$
 for a=1 to len(a$)
   if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
 next a
 print "When you turn everything to lower case and"
 print "replace every vowel with 'e', your input reads:"
 print
 print a$

 This example transforms the input string a bit, using the mid$-function to
 retrieve a character from within the string as well as to change it.

 See also

 left$ and right$.

 -------------------------------------------------------------------------------

 Name

 min() ? return the smaller of its two arguments

 Synopsis

 print min(a,b)

 Description

 Return the minimum of its two argument.

 Example

 dim m(10)
 for a=1 to 1000
   m=min(ran(10),ran(10))
   m(m)=m(m)+1
 next a

 for a=1 to 9
   print a,": ",m(a)
 next a

 For each iteration of the loop, the lower of two random number is recorded. The
 result is printed at the end.

 See also

 max

 -------------------------------------------------------------------------------

 Name

 mod ? compute the remainder of a division

 Synopsis

 print mod(a,b)

 Description

 The mod-function divides its two arguments and computes the remainder. Note,
 that a/b-int(a/b) and mod(a,b) are always equal.

 Example

 clear screen
 print at(10,10) "Please wait ";
 p$="-/"
 for a=1 to 100
   rem  ... do something lengthy here, or simply sleep :-)
   pause(1)
   print at(22,10) mid$(p$,1+mod(a,4))
 next a

 This example executes some time consuming action within a loop (in fact, it
 simply sleeps) and gives the user some indication of progress by displaying a
 turning bar (that's where the mod-function comes into play).

 See also

 int, frac

 -------------------------------------------------------------------------------

 Name

 mouseb ? extract the state of the mousebuttons from a string returned by inkey$

 Synopsis

 inkey$
 print mouseb()
 print mouseb
 a$=inkey$
 print mouseb(a$)

 Description

 The mouseb-function is a helper function for decoding part of the (rather
 complicated) strings, which are returned by the inkey$-function. If a
 mousebutton has been pressed, the mouseb-function returns the number (1,2 or 3)
 of the mousebutton, when it is pressed and returns its negative (-1,-2 or -3),
 when it is released.

 The mouseb-function accepts zero or one arguments. A single argument should be
 a string returned by the inkey$-function; if mouseb is called without any
 arguments, it returns the values from the last call to inkey$, which are stored
 implicitly and internally by yabasic.

 Note

 Note however, that the value returned by the mouseb-function does not reflect
 the current state of the mousebuttons. It rather extracts the information from
 the string passed as an argument (or from the last call to the inkey$-function,
 if no argument is passed). So the value returned by mouseb reflects the state
 of the mousebuttons at the time the inkey$-function has been called; as opposed
 to the time the mouseb-function is called.

 Example

 open window 200,200
 clear screen
 print "Please draw lines; press (and keep it pressed)"
 print "the left mousebutton for the starting point,"
 print "release it for the end-point."
 do
   if (mouseb(release$)=1) press$=release$
   release$=inkey$
   if (mouseb(release$)=-1) then
     line mousex(press$),mousey(press$) to mousex(release$),mousey(release$)
   endif
 loop

 This is a maybe the most simplistic line-drawing program possible, catching
 presses as well as releases of the first mousebutton.

 See also

 inkey$, mousex, mousey and mousemod

 -------------------------------------------------------------------------------

 Name

 mousemod ? return the state of the modifier keys during a mouseclick

 Synopsis

 inkey$
 print mousemod()
 print mousemod
 a$=inkey$
 print mousemod(a$)

 Description

 The mousemod-function is a helper function for decoding part of the (rather
 complicated) strings, which are returned by the inkey$-function if a
 mousebutton has been pressed. It returns the state of the keyboard modifiers
 (shift, ctrl or alt): If the shift-key is pressed, mousemod returns 1, for the
 alt-key 2 and for the ctrl-key 4. If more than one key is pressed, the sum of
 these values is returned, e.g. mousemod returns 5, if shift and ctrl are
 pressed simultaneously.

 The mousemod-function accepts zero or one arguments. A single argument should
 be a string returned by the inkey$-function; if mousemod is called without any
 arguments, it returns the values from the last call to inkey$ (which are stored
 implicitly and internally by yabasic).

 Note

 Please see also the Note within the mouseb-function.

 Example

 open window 200,200
 clear screen
 do
   a$=inkey$
   if (left$(a$,2)="MB") then
     x=mousex(a$)
     y=mousey(a$)
     if (mousemod(a$)=0) then
       circle x,y,20
     else
       fill circle x,y,20
     endif
   endif
 loop

 This program draws a circle, whenever a mousebutton is pressed; the circles are
 filled, when any modifier is pressed, and empty if not.

 See also

 inkey$, mousex, mousey and mouseb

 -------------------------------------------------------------------------------

 Name

 mousex ? return the x-position of a mouseclick

 Synopsis

 inkey$
 print mousex()
 print mousex
 a$=inkey$
 print mousex(a$)

 Description

 The mousex-function is a helper function for decoding part of the (rather
 complicated) strings, which are returned by the inkey$-function; It returns the
 x-position of the mouse as encoded within its argument.

 The mousex-function accepts zero or one arguments. A single argument should be
 a string returned by the inkey$-function; if mousex is called without any
 arguments, it returns the values from the last call to inkey$ (which are stored
 implicitly and internally by yabasic).

 Note

 Please see also the Note within the mouseb-function.

 Example

 open window 200,200
 clear screen
 do
   a$=inkey$
   if (left$(a$,2)="MB") then
     line mousex,0 to mousex,200
   endif
 loop

 This example draws vertical lines at the position, where the mousebutton has
 been pressed.

 See also

 inkey$, mousemod, mousey and mouseb

 -------------------------------------------------------------------------------

 Name

 mousey ? return the y-position of a mouseclick

 Synopsis

 inkey$
 print mousey()
 print mousey
 a$=inkey$
 print mousey(a$)

 Description

 The mousey-function is a helper function for decoding part of the (rather
 complicated) strings, which are returned by the inkey$-function. mousey returns
 the y-position of the mouse as encoded within its argument.

 The mousey-function accepts zero or one arguments. A single argument should be
 a string returned by the inkey$-function; if mousey is called without any
 arguments, it returns the values from the last call to inkey$ (which are stored
 implicitly and internally by yabasic).

 Note

 Please see also the Note within the mouseb-function.

 Example

 open window 200,200
 clear screen
 do
   a$=inkey$
   if (left$(a$,2)="MB") then
     line 0,mousey to 200,mousey
   endif
 loop

 This example draws horizontal lines at the position, where the mousebutton has
 been pressed.

 See also

 inkey$, mousemod, mousex and mouseb

 N

 new curve ? start a new curve, that will be drawn with the line-command
 next ? mark the end of a for loop
 not ? negate an expression; can be written as !
 numparams ? return the number of parameters, that have been passed to a
     subroutine

 Name

 new curve ? start a new curve, that will be drawn with the line-command

 Synopsis

 new curve
 line to x,y

 Description

 The new curve-function starts a new sequence of lines, that will be drawn by
 repeated line to-commands.

 Example

 open window 200,200
 ellipse(100,50,30,60)
 ellipse(150,100,60,30)
 sub ellipse(x,y,xr,yr)
   new curve
   for a=0 to 2*pi step 0.2
     line to x+xr*cos(a),y+yr*sin(a)
   next a
   close curve
 end sub

 This example defines a subroutine ellipse that draws an ellipse. Within this
 subroutine, the ellipse is drawn as a sequence of lines started with the new
 curve command and closed with close curve.

 See also

 line, close curve

 -------------------------------------------------------------------------------

 Name

 next ? mark the end of a for loop

 Synopsis

 for a=1 to 10
 next a

 Description

 The next-keyword marks the end of a for-loop. All statements up to the
 next-keyword will be repeated as specified with the for-clause. Note, that the
 name of the variable is optional; so instead of next a you may write next.

 Example

 for a=1 to 300000
   for b=1 to 21+20*sin(pi*a/20)
     print "*";
   next b
   print
   sleep 0.1
 next a

 This example simply plots a sine-curve until you fall asleep.

 See also

 for

 -------------------------------------------------------------------------------

 Name

 not ? negate an expression; can be written as !

 Synopsis

 if (not a<b) then ?
 bad=!okay

 Description

 The keyword not (or ! for short) is mostly used within conditions (e.g. within
 if- or while-statements). There it is employed to negate the condition or
 expression (i.e. turn TRUE into FALSE and vice versa)

 However not can be used within arithmetic calculations too., simply because
 there is no difference between arithmetic and logical expressions.

 Example

 input "Please enter three ascending numbers: " a,b,c
 if (not (a<b and b<c)) error " the numbers you have entered are not ascending ..."

 See also

 and,or

 -------------------------------------------------------------------------------

 Name

 numparams ? return the number of parameters, that have been passed to a
 subroutine

 Synopsis

 sub foo(a,b,c)
   if (numparams=1) ?
   ?
 end sub

 Description

 Within a subroutine the local variable numparam or numparams contains the
 number of parameters, that have been passed to the subroutine. This information
 can be useful, because the subroutine may have been called with fewer
 parameters than actually declared. The number of values that actually have been
 passed while calling the subroutine, can be found in numparams.

 Note, that arguments which are used in the definition of a subroutine but are
 left out during a call to it (thereby reducing the value of numparams) receive
 a value of 0 or "" (empty string) respectively.

 Example

 a$="123456789"
 print part$(a$,4)
 print part$(a$,3,7)

 sub part$(a$,f,t)
   if (numparams=2) then
     return mid$(a$,f)
   else
     return mid$(a$,f,t-f+1)
   end if
 end sub

 When you run this example, it will print 456789 and 34567. Take a look at the
 subroutine part$, which returns part of the string which has been passed as an
 argument. If (besides the string) two numbers are passed, they define the
 starting and end position of the substring, that will be returned. However, if
 only one number is passed, the rest of the string, starting from this position
 will be returned. Each of these cases is recognized with the help of the
 numparams variable.

 See also

 sub

 O

 on gosub ? jump to one of multiple gosub-targets
 on goto ? jump to one of many goto-targets
 on interrupt ? change reaction on keyboard interrupts
 open ? open a file
 open printer ? open printer for printing graphics
 open window ? open a graphic window
 logical or ? logical or, used in conditions
 or() ? arithmetic or, used for bit-operations

 Name

 on goto ? jump to one of multiple gosub-targets

 Synopsis

 on a gosub foo,bar,baz
   ?
 label foo
   ?
 return

 label bar
   ?
 return

 label baz
   ?
 return

 Description

 The on gosub statement uses its numeric argument (the one between on and gosub)
 to select an element from the list of labels, which follows after the
 gosub-keyword: If the number is 1, the program does a gosub to the first label;
 if the number is 2, to the second and, so on. if the number is zero or less,
 the program continues at the position of the first label; if the number is
 larger than the total count of labels, the execution continues at the position
 of the last label; i.e. the first and last label in the list constitute some
 kind of fallback-slot.

 Note, that the on gosub-command can no longer be considered state of the art;
 people (not me !) may even start to mock you, if you use it.

 Example

 do
   print "Please enter a number between 1 and 3: "
   print
   input "Your choice " a
   on a gosub bad,one,two,three,bad
 loop

 label bad
   print "No. Please between 1 and 3"
 return

 label one
   print "one"
 return

 label two
   print "two"
 return

 label three
   print "three"
 return

 Note, how invalid input (a number less than 1, or larger than 3) is
 automatically detected.

 See also

 goto, on gosub/function>

 -------------------------------------------------------------------------------

 Name

 on goto ? jump to one of many goto-targets

 Synopsis

 on a goto foo,bar,baz
   ?
 label foo
   ?
 label bar
   ?
 label baz
   ?

 Description

 The on goto statement uses its numeric argument (the one between on and goto to
 select an element from the list of labels, which follows after the
 goto-keyword: If the number is 1, the execution continues at the first label;
 if the number is 2, at the second, and so on. if the number is zero or less,
 the program continues at the position of the first label; if the number is
 larger than the total count of labels, the execution continues at the position
 of the last label; i.e. the first and last label in the list constitute some
 kind of fallback-slot.

 Note, that (unlike the goto-command) the on goto-command can no longer be
 considered state of the art; people may (not me !) even start to mock you, if
 you use it.

 Example

 label over
 print "Please Select one of these choices: "
 print
 print "  1 -- show time"
 print "  2 -- show date"
 print "  3 -- exit"
 print
 input "Your choice " a
 on a goto over,show_time,show_date,terminate,over

 label show_time
   print time$()
 goto over

 label show_date
   print date$()
 goto over

 label terminate
 exit

 Note, how invalid input (a number less than 1, or larger than 3) is
 automatically detected; in such a case the question is simply issued again.

 See also

 goto, on gosub/function>

 -------------------------------------------------------------------------------

 Name

 on interrupt ? change reaction on keyboard interrupts

 Synopsis

 on interrupt break
 ?
 on interrupt continue

 Description

 With the on interrupt-command you may change the way, how yabasic reacts on a
 keyboard interrupt; it comes in two variants: on interrupt break and on
 interrupt continue. A keyboard interrupt is produced, if you press ctrl-C on
 your keyboard; normally (and certainly after you have called on interrupt
 break), yabasic will terminate with an error message. However after the command
 on interrupt continue yabasic ignores any keyboard interrupt. This may be
 useful, if you do not want your program being interruptible during certain
 critical operations (e.g. updating of files).

 Example

 print "Please stand by while writing a file with random data ..."
 on interrupt continue
 open "random.data" for writing as #1
 for a=1 to 100
   print #1 ran(100)
   print a," percent done."
   sleep 1
 next a
 close #1
 on interrupt continue

 This program writes a file with 100 random numbers. The on interrupt continue
 command insures, that the program will not be terminated on a keyboard
 interrupt and the file will be written entirely in any case. The sleep-command
 just stretches the process artificially to give you a chance to try a ctrl-C.

 See also

 There is no related command.

 -------------------------------------------------------------------------------

 Name

 open ? open a file

 Synopsis

 open a,"file","r"
 open #a,"file","w"
 open #a,printer
 open "file" for reading as a
 open "file" for writing as #a
 a=open("file")
 a=open("file","r")
 if (open(a,"file")) ?
 if (open(a,"file","w")) ?

 Description

 The open-command opens a file for reading or writing or a printer for printing
 text. open comes in a wide variety of ways; it requires these arguments:

 filenumber

     In the synopsis this is a or #a. In yabasic each file is associated with a
     number between 1 and a maximum value, which depends on the operating
     system. For historical reasons the filenumber can be preceded by a hash ('#
     '). Note, that specifying a filenumber is optional; if it is omitted, the
     open-function will return a filenumber, which should then be stored in a
     variable for later reference. This filenumber can be a simple number or an
     arbitrary complex arithmetic expression, in which case braces might be
     necessary to save yabasic from getting confused.

 filename

     In the synopsis above this is "file". This string specifies the name of the
     file to open (note the important caveat on specifying these filenames).

 accessmode

     In the synopsis this is "r", "w", for reading or for writing. This string
     or clause specifies the mode in which the file is opened; it may be one of:

     "r"

         Open the file for reading (may also be written as for reading). If the
         file does not exist, the command will fail. This mode is the default,
         i.e. if no mode is specified with the open-command, the file will be
         opened with this mode.

     "w"

         Open the file for writing (may also be written as for writing). If the
         file does not exist, it will be created.

     "a"

         Open the file for appending, i.e. what you write to the file will be
         appended after its initial contents. If the file does not exist, it
         will be created.

     "b"

         This letter may not appear alone, but may be combined with the other
         letters (e.g. "rb") to open a file in binary mode (as opposed to text
         mode).

 As you may see from the synopsis, the open-command may either be called as a
 command (without braces) or as a function (with braces). If called as a
 function, it will return the filenumber or zero if the operation fails.
 Therefore the open-function may be used within the condition of an
 if-statement.

 If the open-command fails, you may use peek("error") to retrieve the exact
 nature of the error.

 Furthermore note, that there is another, somewhat separate usage of the
 open-command; if you specify the bareword printer instead of a filename, the
 command opens a printer for printing text. Every text (and only text) you print
 to this file will appear on your printer. Note, that this is very different
 from printing graphics, as can be done with open printer.

 Example

 open "foo.bar" for writing as #1
 print #1 "Hallo !"
 close #1
 if (not open(1,"foo.bar")) error "Could not open 'foo.bar' for reading"
 while(not eof(1))
   line input #1 a$
   print a$
 wend

 This example simply opens the file foo.bar, writes a single line, reopens it
 and reads its contents again.

 See also

 close, print, peek, peek("error") and open printer

 -------------------------------------------------------------------------------

 Name

 open printer ? open printer for printing graphics

 Synopsis

 open printer
 open printer "file"

 Description

 The open printer-command opens a printer for printing graphics. The command
 requires, that a graphic window has been opened before. Everything that is
 drawn into this window will then be sent to the printer too.

 A new piece of paper may be started with the clear window-command; the final
 (or only) page will appear after the close printer-command.

 Note, that you may specify a filename with open printer; in that case the
 printout will be sent to a filename instead to a printer. Your program or the
 user will be responsible for sending this file to the printer afterwards.

 If you use yabasic under Unix, you will need a postscript printer (because
 yabasic produces postscript output). Alternatively you may use ghostscript to
 transform the postscript file into a form suitable for your printer; but that
 is beyond the responsibility of yabasic.

 Example

 open window 200,200
 open printer
 line 0,0 to 200,200
 text 100,100,"Hallo"
 close window
 close printer

 This example will open a window, draw a line and print some text within;
 everything will appear on your printer too.

 See also

 close printer

 -------------------------------------------------------------------------------

 Name

 open window ? open a graphic window

 Synopsis

 open window x,y
 open window x,y,"font"

 Description

 The open window-command opens a window of the specified size. Only one window
 can be opened at any given moment of time.

 An optional third argument specifies a font to be used for any text within the
 window. It can however be changed with any subsequent text-command.

 Example

 for a=200 to 400 step 10
   open window a,a
   for b=0 to a
     line 0,b to a,b
     line b,0 to b,a
   sleep 0.1
   close window
 next a

 See also

 close window, text

 -------------------------------------------------------------------------------

 Name

 or ? logical or, used in conditions

 Synopsis

 if (a or b) ?
 while (a or b) ?

 Description

 Used in conditions (e.g within if or while) to join two expressions. Returns
 true, if either its left or its right or both arguments are true; returns false
 otherwise.

 Example

 input "Please enter a number"
 if (a>9 or a<1) print "a is not between 1 and 9"

 See also

 and,not

 -------------------------------------------------------------------------------

 Name

 or() ? arithmetic or, used for bit-operations

 Synopsis

 x=or(a,b)

 Description

 Used to compute the bitwise or of both its argument. Both arguments are treated
 as binary numbers (i.e. a series of 0 and 1); a bit of the resulting value will
 then be 1, if any of its arguments has 1 at this position in their binary
 representation.

 Note, that both arguments are silently converted to integer values and that
 negative numbers have their own binary representation and may lead to
 unexpected results when passed to or.

 Example

 print or(14,3)

 This will print 15. This result is clear, if you note, that the binary
 representation of 14 and 3 are 1110 and 0011 respectively; this will yield 1111
 in binary representation or 15 as decimal.

 See also

 oand, eor and not

 P

 pause ? pause, sleep, wait for the specified number of seconds
 peek ? retrieve various internal information
 peek$ ? retrieve various internal string-information
 pi ? a constant with the value 3.14159
 poke ? change selected internals of yabasic
 print ? Write to terminal or file
 print color ? print with color
 print colour ? see print color
 putbit ? draw a rectangle of pixels encoded within a string into the graphics
     window
 putscreen ? draw a rectangle of characters into the text terminal

 Name

 pause ? pause, sleep, wait for the specified number of seconds

 Synopsis

 pause 5

 Description

 The pause-command has many different names: You may write pause, sleep or wait
 interchangeably; whatever you write, yabasic will always do exactly the same.

 The pause-command will simply wait for the specified number of seconds. This
 may be a fractional number, so you may well wait less than a second. However,
 if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds, 0.01
 seconds, 0.001 seconds and so on) you will find that at some point yabasic will
 not wait at all. The minimal interval that can be waited depends on the system
 (Unix, Windows) you are using.

 The pause-command cannot be interrupted. However, sometimes you may want the
 wait to be interruptible by simply pressing a key on the keyboard. In such
 cases you should consider using the inkey$-function, with a number of seconds
 as an argument).

 Example

 deg=0
 do
   maxx=44+40*sin(deg)
   for x=1 to maxx
     print "*";
   next x
   pause 0.1+(maxx*maxx/(4*84*84))
   print
   deg=deg+0.1
 loop

 This example draws a sine-curve; due to the pause-statement the speed of
 drawing varies in the same way as the speed of a ball might vary, if it would
 roll along this curve under the influence of gravity.

 See also

 sleep, wait

 -------------------------------------------------------------------------------

 Name

 peek ? retrieve various internal information

 Synopsis

 print peek("foo")
 a=peek(#1)

 Description

 The peek-function has many different and mostly unrelated uses. It is a kind of
 grab-bag for retrieving all kinds of numerical information, internal to yabasic
 . The meaning of the numbers returned be the peek-function depends on the
 string or number passed as an argument.

 peek always returns a number, however the closely related peek$-function
 exists, which may be used to retrieve string information from among the
 internals of yabasic. Finally note, that some of the values which are retrieved
 with peek may even be changed, using the poke-function.

 There are two variants of the peek-function: One expects an integer, positive
 number and is described within the first entry of the list below. The other
 variant expects one of a well defined set of strings as described in the second
 and all the following entries of the list below.

 peek(a)

     Read a single character from the file a (which must be open of course).

 peek("argument")

     Return the number of arguments, that have been passed to yabasic at
     invocation time. E.g. if yabasic has been called like this: yabasic foo.yab
     bar baz, then peek("argument") will return 2. This is because foo.yab is
     treated as the name of the program to run, whereas bar and baz are
     considered arguments to the program, which are passed on the command line.
     Note, that for windows-users, who tend to click on the icon (as opposed to
     starting yabasic on the command line), this peekwill mostly return 0.

     The function peek("argument") can be written as peek("arguments") too.

     You will want to check out the corresponding function peek$("argument") to
     actually retrieve the arguments. Note, that each call to peek$("argument")
     reduces the number returned by peek("argument").

 peek("error")

     Return a number specifying the nature of the last error in an open- or
     seek-statement. Normally an error within an open-statement immediately
     terminates your program with an appropriate error-message, so there is no
     chance and no need to learn more about the nature of the error. However, if
     you use open as a condition (e.g. if (open(#1,"foo")) ?) the outcome
     (success or failure) of the open-operation will determine, if the condition
     evaluates to true or false. If now such an operation fails, your program
     will not be terminated and you might want to learn the reason for failure.
     This reason will be returned by peek("error") (as a number) or by peek$
     ("error") (as a string)

     The table below shows the various error codes; the value returned by peek$
     ("error") explains the nature of the error. Note, that the codes 10,11 and
     12 refer to the seek-command.

     Table 7.1. Error codes

     +-------------------------------------------------------------------------+
     |  peek   |peek$("error")|                  Explanation                   |
     |("error")|              |                                                |
     |---------+--------------+------------------------------------------------|
     |    2    |Stream already|Do not try to open one and the same filenumber  |
     |         |in use        |twice; rather close it first.                   |
     |---------+--------------+------------------------------------------------|
     |         |'x' is not a  |The optional filemode argument, which may be    |
     |    3    |valid filemode|passed to the open-function, has an invalid     |
     |         |              |value                                           |
     |---------+--------------+------------------------------------------------|
     |    4    |could not open|The open-call did not work, no further          |
     |         |'foo'         |explanation is available.                       |
     |---------+--------------+------------------------------------------------|
     |         |reached       |You have opened more files than your operating  |
     |    5    |maximum number|system permits.                                 |
     |         |of open files |                                                |
     |---------+--------------+------------------------------------------------|
     |         |cannot open   |The commands open printer and open #1,printer   |
     |         |printer:      |both open a printer (refer to their description |
     |    6    |already       |for the difference). However, only one can be   |
     |         |printing      |active at a time; if you try to do both at the  |
     |         |graphics      |same time, you will receive this error.         |
     |---------+--------------+------------------------------------------------|
     |    7    |could not open|Well, it simply did not work.                   |
     |         |line printer  |                                                |
     |---------+--------------+------------------------------------------------|
     |    9    |invalid stream|An attempt to use an invalid (e.g. negative)    |
     |         |number        |stream number; example: open(-1,"foo")          |
     |---------+--------------+------------------------------------------------|
     |         |could not     |                                                |
     |   10    |position      |seek did not work.                              |
     |         |stream x to   |                                                |
     |         |byte y        |                                                |
     |---------+--------------+------------------------------------------------|
     |   11    |stream x not  |You have tried to seek within a stream, that has|
     |         |open          |not been opened yet.                            |
     |---------+--------------+------------------------------------------------|
     |         |seek mode 'x' |The argument, which has been passed to seek is  |
     |   12    |is none of    |invalid.                                        |
     |         |begin,end,here|                                                |
     +-------------------------------------------------------------------------+

 peek("fontheight")

     Return the height of the font used within the graphic window. If none is
     open, this peek will return the height of the last font used or 10, if no
     window has been opened yet.

 peek("screenheight")

     Return the height in characters of the window, wherein yabasic runs. If you
     have not called clear screen yet, this peekwill return 0, regardless of the
     size of your terminal.

 peek("screenwidth")

     Return the width in characters of the window, wherein yabasic runs. If you
     have not called clear screen yet, this peekwill return 0, regardless of the
     size of your terminal.

 peek("secondsrunning")

     Return the number of seconds that have passed since the start of yabasic.

 peek("millisrunning")

     Return the number of milliseconds, that have passed since the start of
     yabasic.

 peek("version")

     Return the version number of yabasic, e.g. 2.77. See also the related peek$
     ("version"), which returns nearly the same information (plus the
     patchlevel) as a string, e.g. "2.77.1".

 peek("winheight")

     Return the height of the graphic-window in pixels. If none is open, this
     peek will return the height of the last window opened or 100, if none has
     been opened yet.

 peek("winwidth")

     Return the width of the graphic-window in pixels. If none is open, this
     peek will return the width of the last window opened or 100, if none has
     been opened yet.

 peek("isbound")

     Return true, if the executing yabasic-program is part of a standalone
     program; see the section about creating a standalone-program for details.

 peek("version")

     Return the version number of yabasic (e.g. 2.72).

 Example

 open "foo" for reading as #1
 open "bar" for writing as #2
 while(not eof(#1))
   poke #2,chr$(peek(#1));
 wend

 This program will copy the file foo byte by byte to bar.

 Note, that each peek does something entirely different, and only one has been
 demonstrated above. Therefore you need to make up examples yourself for all the
 other peeks.

 See also

 peek$, poke, open

 -------------------------------------------------------------------------------

 Name

 peek$ ? retrieve various internal string-information

 Synopsis

 print peek$("foo")

 Description

 The peek$-function has many different and unrelated uses. It is a kind of
 grab-bag for retrieving all kinds of string information, internal to yabasic;
 the exact nature of the strings returned be the peek$-function depends on the
 string passed as an argument.

 peek$ always returns a string, however the closely related peek-function
 exists, which may be used to retrieve numerical information from among the
 internals of yabasic. Finally note, that some of the values which are retrieved
 with peek$ may even be changed, using the poke-function.

 The following list shows all possible arguments to peek$:

 peek$("infolevel")

     Returns either "debug", "note", "warning", "error" or "fatal", depending on
     the current infolevel. This value can be specified with an option on the
     command line or changed during the execution of the program with the
     corresponding poke; however, normally only the author of yabasic (me !)
     would want to change this from its default value "warning".

 peek$("textalign")

     Returns one of nine possible strings, specifying the default alignment of
     text within the graphics-window. The alignment-string returned by this peek
     describes, how the text-command aligns its string-argument with respect to
     the coordinates supplied. However, this value does not apply, if the
     text-command explicitly specifies an alignment. Each of these strings is
     two characters long. The first character specifies the horizontal alignment
     and can be either l, r or c, which stand for left, right or center. The
     second character specifies the vertical alignment and can be one of t, b or
     c, which stand for top, bottom or center respectively.

     You may change this value with the corresponding command poke
     "textalign",?; the initial value is lb, which means the top of the left and
     the top edge if the text will be aligned with the coordinates, that are
     specified within the text-command.

 peek$("windoworigin")

     This peek returns a two character string, which specifies the position of
     the origin of the coordinate system of the window; this string might be
     changed with the corresponding command poke "windoworigin",x,y or specified
     as the argument of the origin command; see there for a detailed description
     of the string, which might be returned by this peek.

 peek$("program_name")

     Returns the name of the yabasic-program that is currently executing;
     typically this is the name, that you have specified on the commandline, but
     without any path-components. So this peek$ might return foo.yab. As a
     special case when yabasic has been invoked without the name of a program to
     be executed this peek will return the literal strings standard input or,
     when also the option -e has been specified, command line. See also peek$
     ("program_file_name") and peek$("interpreter_path") for related
     information.

 peek$("program_file_name")

     Returns the full file-name of the yabasic-program that is currently
     executing; typically this is the name, that you have specified on the
     commandline, including any path-components. For the special case, that you
     have bound your yabasic-program with the interpreter to a single standalone
     executable, this peek$ will return its name. See also peek$("program_name")
     and peek$("interpreter_path") for related information.

 peek$("interpreter_path")

     Return the full file-name of the yabasic-interpreter that is currently
     executing your program; typically this will end on yabasic or yabasic.exe
     depending on your platform and the path will be where you installed yabasic
     . For bound programs (see creating a standalone-program) however, this may
     be different and will include whatever you specified during the bind
     -command.

     See also peek$("program_name") and peek$("program_file_name") for related
     information. Employing these, it would be possible for a yabasic-program to
     start itself: system(peek$("interpreter_path") + " " + peek$
     ("program_file_name")). Of course, in this simple form this would be a bad
     idea, because this would start concurrent instances of yabasic without end.

 peek$("error")

     Return a string describing the nature of the last error in an open- or
     seek-statement. See the corresponding peek("error") for a detailed
     description.

 peek$("library")

     Return the name of the library, this statement is contained in. See the
     import-command for a detailed description or for more about libraries.

 peek$("version")

     Version of yabasic as a string; e.g. 2.77.1. See also the related peek
     ("version"), which returns nearly the same information (minus the
     patchlevel) as a number, e.g. 2.77.

 peek$("os")

     This peek returns the name of the operating system, where your program
     executes. This can be either windows or unix.

 peek$("font")

     Return the name of the font, which is used for text within the graphic
     window; this value can be specified as the third argument to the open
     window-command.

 peek$("env","NAME")

     Return the environment variable specified by NAME (which may be any string
     expression). Which kind of environment variables are available on your
     system depends, as well as their meaning, on your system; however typing
     env on the command line will produce a list (for Windows and Unix alike).
     Note, that peek$("env",...) can be written as peek$("environment",...) too.

 peek$("argument")

     Return one of the arguments, that have been passed to yabasic at invocation
     time (the next call will return the the second argument, and so on). E.g.
     if yabasic has been called like this: yabasic foo.yab bar baz, then the
     first call to peek$("argument") will return bar. This is because foo.yab is
     treated as the name of the program to run, whereas bar and baz are
     considered arguments to this program, which are passed on the command line.
     The second call to peek$("argument") will return baz. Note, that for
     windows-users, who tend to click on the icon (as opposed to starting
     yabasic on the command line), this peekwill mostly return the empty string.

     Note, that peek$("argument") can be written as peek$("arguments").

     Finally you will want to check out the corresponding function peek
     ("argument").

 Example

 print "You have supplied these arguments: "
 while(peek("argument"))
   print peek("argument"),peek$("argument")
 wend

 If you save this program in a file foo.yab and execute it via yabasic t.yab a b
 c (for windows users: please use the command line for this), your will get this
 output:

 3a
 2b
 1c

 See also

 peek, poke, open

 -------------------------------------------------------------------------------

 Name

 pi ? a constant with the value 3.14159

 Synopsis

 print pi

 Description

 pi is 3.14159265359 (well at least for yabasic); do not try to assign to pi
 (e.g. pi=22/7) this would not only be mathematically dubious, but would also
 result in a syntax error.

 Example

 for a=0 to 180
   print "The sine of ",a," degrees is ",sin(a*pi/180)
 next a

 This program uses pi to transform an angle from degrees into radians.

 See also

 euler

 -------------------------------------------------------------------------------

 Name

 poke ? change selected internals of yabasic

 Synopsis

 poke "foo","bar"
 poke "foo",baz
 poke #a,"bar"
 poke #a,baz

 Description

 The poke-command may be used to change details of yabasic's behaviour. Like the
 related function peek, poke does many different things, depending on the
 arguments supplied.

 Here are the different things you can do with poke:

 poke 5,a

     Write the given byte (a in the example above) to the specified stream (5#a
     in the example).

     See also the related function function peek(1).

 poke "dump","filename.dump"

     Dump the internal form of your basic-program to the named file; this is
     only useful for debugging the internals of yabasic itself.

     The second argument ("filename.dump" in the example) should be the name of
     a file, that gets overwritten with the dump, please be careful.

 poke "fontheight",12

     This poke changes the default fontheight. This can only have an effect, if
     the fonts given in the commands text or open window do not specify a
     fontheight on their own.

 poke "font","fontname"

     This poke specifies the default font. This can only have an effect, if you
     do not supply a fontname with the commands text or open window.

 poke "infolevel","debug"

     Change the amount of internal information, that yabasic outputs during
     execution.

     The second argument can be either "debug", "note", "warning", "error" or
     "fatal". However, normally you will not want to change this from its
     default value "warning".

     See also the related peek$("infolevel").

 poke "random_seed",42

     Set the seed for the random number generator; if you do this, the ran
     -function will return the same sequence of numbers every time the program
     is started.

 poke "stdout","some text"

     Send the given text to standard output. Normally one would use print for
     this purpose; however, sending e.g. control characters to your terminal is
     easier with this poke.

 poke "textalign","cc"

     This poke changes the default alignment of text with respect to the
     coordinates supplied within the text-command. However, this value does not
     apply, if the text-command explicitly specifies an alignment. The second
     argument ("cc" in the example) must always be two characters long; the
     first character can be one of l (left), r (right) or c (center); the second
     character can be either t (top), b (bottom) or c (center); see the
     corresponding peek$("textalign") for a detailed description of this
     argument.

 poke "windoworigin","lt"

     This poke moves the origin of the coordinate system of the window to the
     specified position. The second argument ("lt" in the example) must always
     be two characters long; the first character can be one of l (left), r (
     right) or c (center); the second character can be either t (top), b (bottom
     ) or c (center). Together those two characters specify the new position of
     the coordinate-origin. See the corresponding peek$("windoworigin") for a
     more in depth description of this argument.

 Example

 print "Hello, now you will see, how much work"
 print "a simple for-loop involves ..."
 input "Please press return " a$
 poke "infolevel","debug"
 for a=1 to 10:next a

 This example only demonstrates one of the many pokes, which are described
 above: The program switches the infolevel to debug, which makes yabasic produce
 a lot of debug-messages during the subsequent for-loop.

 See also

 peek, peek$

 -------------------------------------------------------------------------------

 Name

 print ? Write to terminal or file

 Synopsis

 print "foo",a$,b
 print "foo",a$,b;
 print #a "foo",a$
 print #a "foo",a$;
 print foo using "##.###"
 print reverse "foo"
 print at(10,10) a$,b
 print @(10,10) a$,b
 print color("red","blue") a$,b
 print color("magenta") a$,b
 print color("green","yellow") at(5,5) a$,b

 Description

 The print-statement outputs strings or characters, either to your terminal
 (also known as console) or to an open file.

 To understand all those uses of the print-statement, let's go through the
 various lines in the synopsis above:

 print "foo",a$,b

     Print the string foo as well as the contents of the variables a$ and b onto
     the screen, silently adding a newline.

 print "foo",a$,b;

     (Note the trailing semicolon !) This statement does the same as the one
     above; only the implicit newline is skipped, which means that the next
     print-statement will append seamlessly.

 print #a "foo",a$

     This is the way to write to files. The file with the number a must be open
     already, an implicit newline is added. Note the file-number #a, which
     starts with a hash ('#') amd is separated from the rest of the statement by
     a space only. The file-number (contained in the variable a) must have been
     returned by a previous open-statement (e.g. a=open("bar")).

 print #a "foo",a$;

     The same as above, but without the implicit newline.

 print foo using "##.###"

     Print the number foo with as many digits before and after the decimal dot
     as given by the number of '#'-signs. See the entries for using and str$ for
     a detailed description of this format.

 print reverse "foo"

     As all the print-variants to follow, this form of the print-statement can
     only be issued after clear screen has been called. The strings and numbers
     after the reverse-clause are simply printed inverse (compared to the normal
     print-statement).

 print at(10,10) a$,b

     Print at the specified (x,y)-position. This is only allowed after clear
     screen has been called. You may want to query peek$("screenwidth") or peek$
     ("screenheight") to learn the actual size of your screen. You may add a
     semicolon to suppress the implicit newline.

 print @(10,10) a$,b

     This is exactly the same as above, however, at may be written as @.

 print color("red","blue") at(5,5) a$,b

     Print with the specified fore- ("red") and background ("blue") color (or
     colour). The possible values are "black", "white", "red", "blue", "green",
     "yellow", "cyan" or "magenta". Again, you need to call clear screen first
     and add a semicolon if you want to suppress the implicit newline.

 print color("magenta") a$,b

     You may specify the foreground color only.

 print color("green","yellow") a$,b

     A color and a position (in this sequence, not the other way around) may be
     specified at once.

 Example

 clear screen
 columns=peek("screenwidth")
 lines=peek("screenheight")
 dim col$(7)
 for a=0 to 7:read col$(a):next a
 data "black","white","red","blue","green","yellow","cyan","magenta"

 for a=0 to 2*pi step 0.1
   print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*cos(a)+0.9)/2) "*"
   i=i+1
 next a

 This example draws a colored ellipse within the text window.

 See also

 at, print color, input, clear screen, using, ;

 -------------------------------------------------------------------------------

 Name

 print color ? print with color

 Synopsis

 print color(fore$) text$
 print color(fore$,back$) text$

 Description

 Not a separate command, but part of the print-command; may be included just
 after print and can only be issued after clear screen has been executed.

 color() takes one or two string-arguments, specifying the color of the text and
 (optionally) the background.

 The one or two strings passed to color() can be one of these: "black", "white",
 "red", "blue", "green", "yellow", "cyan" and "magenta" (which can be
 abbreviated as "bla", "whi", "red", "blu", "gre", "yel", "cya" and "mag"
 respectively).

 color() can only be used, if clear scren has been issued at least once.

 Note, that color() can be written as colour() too.

 Example

 clear screen
 dim col$(7):for a=0 to 7:read col$(a):next a
 do
   print color(col$(ran(7)),col$(ran(7))) " Hallo ";
   pause 0.01
 loop
 data "black","white","red","blue"
 data "green","yellow","cyan","magenta"

 This prints the word " Hallo " in all colors across your screen.

 See also

 print, clear screen, at

 -------------------------------------------------------------------------------

 Name

 print colour ? see print color

 Synopsis

 print colour(fore$) text$
 print colour(fore$,back$) text$

 See also

 color

 -------------------------------------------------------------------------------

 Name

 putbit ? draw a rectangle of pixels encoded within a string into the graphics
 window

 Synopsis

 open window 200,200
 ?
 a$=getbit(20,20,50,50)
 ?
 putbit a$,30,30
 putbit a$ to 30,30
 putbit a$,30,30,"or"

 Description

 The putbit-command is the counterpart of the getbit$-function. putbit requires
 a string as returned by the getbit-function. Such a string contains a rectangle
 from the graphic window; the putbit-function puts such a rectangular region
 back into the graphic-window.

 Note, that the putbit-command currently accepts a fourth argument. However only
 the string value "or" is supported here. The effect is, that only those pixel,
 which are set in the string will be set in the graphic window. Those pixels,
 which are not set in the string, will not change in the window (as opposed to
 being cleared).

 Example

 c$="rgb 21,21:0000000000000000000000000000000000000000000000000000000000000032c80000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c8c8ff000032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c8000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

 open window 200,200

 do
   x=ran(220)-10
   y=ran(220)-10
   putbit c$,x,y,"transparent"
 loop

 This program uses a precanned string (containing the image of a blue circle
 with a yellow centre) and draws it repeatedly into the graphic-window. The mode
 "transparent" ensures, that no pixels will be cleared.

 There are two possible values for the third argument of putbit. Both modes
 differ in the way, they replace (or not) any pixels from the window with pixels
 from the bitmap having the background colour.

 transparent or t

     With this mode the pixels from the window will be kept, if the bitmap
     contains pixels with background colour at this position; i.e. the bitmap is
     transparent

 solid or s

     With this mode the pixels from the window will be overpainted with the
     pixels from the bitmap in any case; i.e. the bitmap is solid

 If you omit this argument, the default transparent applies.

 See also

 getbit$, open window

 -------------------------------------------------------------------------------

 Name

 putscreen ? draw a rectangle of characters into the text terminal

 Synopsis

 clear screen
 ?
 a$=getscreen$(5,5,10,10)
 ?
 putscreen a$,7,7

 Description

 The putscreen-command is the counterpart of the getscreen$-function. putscreen
 requires a string as returned by the getscreen-function. Such a string contains
 a rectangular detail from the terminal; the putscreen-function puts such a
 region back into the terminal-window.

 Note, that clear screen must have been called before.

 Example

 clear screen
 for a=1 to 200
   print color("red") "Hallo !";
   print color("blue") "Welt !";
 next a
 r$=getscreen$(0,0,20,20)
 for x=0 to 60
   putscreen r$,x,0
   sleep 0.1
 next x

 This example prints the string "Hallo !Welt !" all over the screen and then
 moves a rectangle from one side to the other.

 See also

 getscreen$, clear screen

 R

 ran() ? return a random number
 read ? read data from data-statements
 rectangle ? draw a rectangle
 redim ? create an array prior to its first use. A synonym for dim
 rem ? start a comment
 repeat ? start a repeat-loop
 restore ? reposition the data-pointer
 return ? return from a subroutine or a gosub
 reverse ? print reverse (background and foreground colors exchanged)
 right$() ? return (or change) the right end of a string
 rinstr() ? find the rightmost occurrence of one string within the other
 rtrim$() ? trim spaces at the right end of a string

 Name

 ran() ? return a random number

 Synopsis

 print ran()
 x=ran(y)

 Description

 The ran-function returns a random number. If no argument is given, the number
 returned is in the range from 0 to 1; where only 0 is a possible value; 1 will
 never be returned. If an argument is supplied, the number returned will be in
 the range from 0 up to this argument, whereas this argument itself is not a
 possible return value. Regardless of the range, ran is guaranteed to have
 exactly 2**30 different return values.

 If you call ran multiple times during your program, the sequence of random
 numbers will be different each time you invoke your program; however, if, e.g.
 for testing you prefer to always have the same sequence of random numbers you
 may issue poke "random_seed",123.

 Example

 clear screen
 c=peek("screenwidth")-1
 l=peek("screenheight")

 dim col$(8)
 for a=0 to 7:read col$(a):next a
 data "black","white","red","blue","green","yellow","cyan","magenta"

 do
   x=ran(c)
   y=l-ran(l*exp(-32*((x/c-1/2)**2)))
   i=i+1
   print color(col$(mod(i,8))) at(x,y) "*";
 loop

 This example will print a colored bell-curve.

 See also

 int

 -------------------------------------------------------------------------------

 Name

 read ? read data from data-statements

 Synopsis

 read a$,a
 ?
 data "Hello !",7

 Description

 The read-statement retrieves literal data, which is stored within
 data-statements elsewhere in your program.

 Example

 read num
 dim col$(num)
 for a=1 to num:read col$(a):next a
 clear screen
 print "These are the colours known to yabasic:
 for a=1 to num
   print colour(col$(a)) col$(a)
 next a

 data 8,"black","white","red","blue"
 data "green","yellow","cyan","magenta"

 This program prints the names of the colors known to yabasic in those very
 colors.

 See also

 data, restore

 -------------------------------------------------------------------------------

 Name

 rectangle ? draw a rectangle

 Synopsis

 open window 100,100
 rectangle 10,10 to 90,90
 rectangle 20,20,80,80
 rect 20,20,80,80
 box 30,30,70,70
 clear rectangle 30,30,70,70
 fill rectangle 40,40,60,60
 clear fill rectangle 60,60,40,40

 Description

 The rectangle-command (also known as box or rect, for short) draws a rectangle;
 it accepts four parameters: The x- and y-coordinates of two facing corners of
 the rectangle. With the optional clauses clear and fill (which may appear
 together and in any sequence) the rectangle can be cleared and filled
 respectively.

 Example

 open window 200,200
 c=1
 do
   for phi=0 to pi step 0.1
     if (c) then
       rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
     else
       clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
     endif
     sleep 0.1
   next phi
   c=not c
 loop

 This example draws a nice animated pattern; watch it for a couple of hours, to
 see how it develops.

 See also

 open window, open printer, line, circle, triangle

 -------------------------------------------------------------------------------

 Name

 redim ? create an array prior to its first use. A synonym for dim

 Synopsis

 See the dim-command.

 Description

 The redim-command does exactly the same as the dim-command; it is just a
 synonym. redim has been around in older versions of basic (not even yabasic)
 for many years; therefore it is supported in yabasic for compatibility reasons.

 Please refer to the entry for the dim-command for further information.

 -------------------------------------------------------------------------------

 Name

 rem ? start a comment

 Synopsis

 rem  Hey, this is a comment
 #    the hash-sign too (at beginning of line)
 // even the double slash
 ' and the single quote (at beginning of line)
 print "Not a comment" #    This is an error !!
 print "Not a comment"://   But this is again a valid comment
 print "Not a comment" //   even this.
 print "Not a comment" rem  and this !

 Description

 rem introduces a comment (like # or //), that extends up to the end of the
 line.

 Those comments do not even need a colon (':') in front of them; they (rem, #, '
 (single quite) and //) all behave alike except for # and ', which may only
 appear at the very beginning of a line; therefore the fourth example in the
 synopsis above (print "Not a comment" # This is an error !!) is indeed an
 error.

 Note, that rem is an abbreviation for remark. remark however is not a valid
 command in yabasic.

 Finally note, that a comment introduced with '#' may have a special meaning
 under unix; see the entry for # for details.

 Example

 #
 rem   comments on data structures
 #     are more useful than
 //    comments on algorithms.
 rem

 This program does nothing, but in a splendid and well commented way.

 See also

 #, //

 -------------------------------------------------------------------------------

 Name

 repeat ? start a repeat-loop

 Synopsis

 repeat
   ?
 until (?)

 Description

 The repeat-loop executes all the statements up to the final until-keyword over
 and over. The loop is executed as long as the condition, which is specified
 with the until-clause, becomes true. By construction, the statements within the
 loop are executed at least once.

 Example

 x=0
 clear screen
 print "This program will print the numbers from 1 to 10"
 repeat
   x=x+1
   print x
   print "Press any key for the next number, or 'q' to quit"
   if (inkey$="q") break
 until(x=10)

 This program is pretty much useless, but self-explanatory.

 See also

 until, break, while, do

 -------------------------------------------------------------------------------

 Name

 restore ? reposition the data-pointer

 Synopsis

 read a,b,c,d,e,f
 restore
 read g,h,i
 restore foo
 data 1,2,3
 label foo
 data 4,5,6

 Description

 The restore-command may be used to reset the reading of data-statements, so
 that the next read-statement will read data from the first data-statement.

 You may specify a label with the restore-command; in that case, the next
 read-statement will read data starting at the given label. If the label is
 omitted, reading data will begin with the first data-statement within your
 program.

 Example

 input "Which language (german/english) ? " l$
 if (instr("german",l$)>0) then
   restore german
 else
   restore english
 endif

 for a=1 to 3
   read x,x$
   print x,"=",x$
 next a

 label english
 data 1,"one",2,"two",3,"three"
 label german
 data 1,"eins",2,"zwei",3,"drei"

 This program asks to select one of those languages known to me (i.e. english or
 german) and then prints the numbers 1,2 and 3 and their textual equivalents in
 the chosen language.

 See also

 read, data, label

 -------------------------------------------------------------------------------

 Name

 return ? return from a subroutine or a gosub

 Synopsis

 gosub foo
 ?
 label foo
 ?
 return

 sub bar(baz)
   ?
   return quertz
 end sub

 Description

 The return-statement serves two different (albeit somewhat related) purposes.
 The probably more important use of return is to return control from within a
 subroutine to the place in your program, where the subroutine has been called.
 If the subroutine is declared to return a value, the return-statement might be
 accompanied by a string or number, which constitutes the return value of the
 subroutine.

 However, even if the subroutine should return a value, the return-statement
 need not carry a value; in that case the subroutine will return 0 or the empty
 string (depending on the type of the subroutine). Moreover, feel free to place
 multiple return-statements within your subroutine; it's a nice way of
 controlling the flow of execution.

 The second (but historically first) use of return is to return to the position,
 where a prior gosub has left off. In that case return may not carry a value.

 Example

 do
   read a$
   if (a$="") then
     print
     end
   endif
   print mark$(a$)," ";
 loop

 data "The","quick","brown","fox","jumped"
 data "over","the","lazy","dog",""

 sub mark$(a$)
   if (instr(lower$(a$),"q")) return upper$(a$)
   return a$
 end sub

 This example features a subroutine mark$, that returns its argument in upper
 case, if it contains the letter "q", or unchanged otherwise. In the test-text
 the word quick will end up being marked as QUICK.

 The example above demonstrates return within subroutines; please see gosub for
 an example of how to use return in this context.

 See also

 sub, gosub

 -------------------------------------------------------------------------------

 Name

 reverse ? print reverse (background and foreground colors exchanged)

 Synopsis

 clear screen
 ?
 print reverse "foo"

 Description

 reverse may be used to print text in reverse. reverse is not a separate
 command, but part of the print-command; it may be included just after the print
 and can only be issued once that clear screen has been issued.

 Example

 clear screen

 print "1 ";
 c=3
 do
   prim=true
   for a=2 to sqrt(c)
     if (frac(c/a)=0) then
       prim=false
       break
     endif
   next a
   if (prim) then
     print
     print reverse c;
   else
     print c;
   endif
   print " ";
   c=c+1
 loop

 This program prints numbers from 1 on and marks each prime number in reverse.

 See also

 at, print color, print, clear screen

 -------------------------------------------------------------------------------

 Name

 right$() ? return (or change) the right end of a string

 Synopsis

 print right$(a$,2)
 right$(b$,2)="baz"

 Description

 The right$-function requires two arguments (a string and a number) and returns
 the part from the right end of the string, whose length is specified by its
 second argument. So, right$ simply returns the requested number of chars from
 the right end of the given string.

 Note, that the right$-function can be assigned to, i.e. it may appear on the
 left hand side of an assignment. In this way it is possible to change a part of
 the variable used within the right$-function. Note, that that way the length of
 the string cannot be changed, i.e. characters might be overwritten, but not
 added. For an example see below.

 Example

 print "Please enter a length either in inch or centimeter"
 print "please add 'in' or 'cm' to mark the unit."
 input "Length: " a$
 if (right$(a$,2)="in") then
    length=val(a$)*2.56
 elsif (right$(a$,2)="cm") then
    length=val(a$)
 else
    error "Invalid input: "+a$
 endif

 This program allows the user to enter a length qualified with a unit (either
 inch or centimeter).

 This second example demonstrates the capability to assign to the
 right$-function.

 a$="Heiho World !"
 print a$
 right$(a$,7)="dwarfs."
 print a$

 See also

 right$ and mid$

 -------------------------------------------------------------------------------

 Name

 rinstr() ? find the rightmost occurrence of one string within the other

 Synopsis

 pos=rinstr("Thequickbrownfox","equi")
 pos=rinstr(a$,b$,x)

 Description

 The rinstr-function accepts two string-arguments and tries to find the second
 within the first. However, unlike the instr, the rinstr-function finds the
 rightmost (or last) occurrence of the string; whereas the instr-function finds
 the leftmost (or first) occurrence. In any case however, the position is
 counted from the left.

 If you supply a third, numeric argument to the rinstr-function, it will be used
 as a starting point for the search. Therefore rinstr("abcdeabcdeabcde","e",8)
 will return 5, because the search for an "e" starts at position 8 and finds the
 first one at position 5.

 Example

 print rinstr("foofoofoobar","foo")

 This simple example will print 7, because it finds the rightmost among the
 three occurrences of foo within the string. Note, that

 print instr("foofoofoobar","foo")

 would have printed 1.

 See also

 instr

 -------------------------------------------------------------------------------

 Name

 rtrim$() ? trim spaces at the right end of a string

 Synopsis

 a$=rtrim$(b$)

 Description

 The rtrim$-function removes all whitespace from the right end of a string and
 returns the result.

 Example

 open 1,"foo"
 dim lines$(100)
 l=1
 while(not eof(1))
   input #1 a$
   a$=rtrim$(a$)
   if (right$(line$,1)="\") then
     line$=line$+" "+a$
   else
     lines$(l)=line$
     l=l+1
     line$=a$
   endif
 end while
 print "Read ",l," lines"

 This example reads the file foo allowing for continuation lines, which are
 marked by a  which appears as the last character on a line. For convenience
 whitespace at the right end of a line is trimmed with rtrim.

 See also

 ltrim$, trim$

 S

 screen ? as clear screen clears the text window
 seek() ? change the position within an open file
 sig() ? return the sign of its argument
 sin() ? return the sine of its single argument
 sleep ? pause, sleep, wait for the specified number of seconds
 split() ? split a string into many strings
 sqr() ? compute the square of its argument
 sqrt() ? compute the square root of its argument
 static ? preserves the value of a variable between calls to a subroutine
 step ? specifies the increment step in a for-loop
 str$() ? convert a number into a string
 sub ? declare a user defined subroutine
 switch ? select one of many alternatives depending on a value
 system() ? hand a statement over to your operating system and return its
     exitcode
 system$() ? hand a statement over to your operating system and return its
     output

 Name

 screen ? as clear screen clears the text window

 Synopsis

 clear screen

 Description

 The keyword screen appears only within the sequence clear screen; please see
 there for a description.

 See also

 clear screen

 -------------------------------------------------------------------------------

 Name

 seek() ? change the position within an open file

 Synopsis

 open 1,"foo"
 seek #1,q
 seek #1,x,"begin"
 seek #1,y,"end"
 seek #1,z,"here"

 Description

 The seek-command changes the position, where the next input (or peek) statement
 will read from an open file. Usually files are read from the beginning to the
 end sequentially; however sometimes you may want to depart from this simple
 scheme. This can be done with the seek-command, allowing you to change the
 position, where the next piece of data will be read from the file.

 seek accepts two or three arguments: The first one is the number of an already
 open file. The second one is the position where the next read from the file
 will start. The third argument is optional and specifies the the point from
 where the position (the second argument) will count. It can be one of:

 begin

     Count from the beginning of the file.

 end

     Count from the end of the file.

 here

     Count from the current position within the file.

 Example

 open #1,"count.dat","w"
 for a=1 to 10
   print #1,"00000000";
   if (a<10) print #1,";";
 next a

 dim count(10)
 do
   x=int(ran(10))
   i=i+1
   if (mod(i,1000)=0) print ".";
   count(x)=count(x)+1
   curr$=right$("00000000"+str$(count(x)),8)
   seek #1,9*x,"begin"
   print #1,curr$;
 loop

 This example increments randomly one of ten counters (in the array count());
 however, the result is always kept and updated within the file count.dat, so
 even in case of an unexpected interrupt, the result will not be lost.

 See also

 tell, open, print, peek

 -------------------------------------------------------------------------------

 Name

 sig() ? return the sign of its argument

 Synopsis

 a=sig(b)

 Description

 Return +1, -1 or 0, if the single argument is positive, negative or zero.

 Example

 clear screen
 dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
 do
   num=ran(100)-50
   print color(c$(2+sig(num))) num
 loop

 This program prints an infinite sequence of random number; positive numbers are
 printed in green, negative numbers are printed red (an exact zero would be
 printed white). (With a little extra work, this program could be easily
 extended into a brokerage system)

 See also

 abs, int, frac

 -------------------------------------------------------------------------------

 Name

 sin() ? return the sine of its single argument

 Synopsis

 y=sin(angle)

 Description

 The sin-function expects an angle (in radians, not degrees) and returns its
 sine.

 Example

 open window 200,200
 new curve
 for phi=0 to 2*pi step 0.1
   line to 100+90*sin(phi),100+90*cos(phi)
 next phi
 close curve

 This program draws a circle (ignoring the existence of the circle-command).

 See also

 asin, cos

 -------------------------------------------------------------------------------

 Name

 sleep ? pause, sleep, wait for the specified number of seconds

 Synopsis

 sleep 4

 Description

 The sleep-command has many different names: You may write pause, sleep or wait
 interchangeably; whatever you write, yabasic will always do exactly the same.

 Therefore you should refer to the entry for the pause-function for further
 information.

 -------------------------------------------------------------------------------

 Name

 split() ? split a string into many strings

 Synopsis

 dim w$(10)
 ?
 num=split(a$,w$())
 num=split(a$,w$(),s$)

 Description

 The split-function requires a string (containing the text to be split), a
 reference to a string-array (which will receive the resulting strings, i.e. the
 tokens) and an optional string (with a set of characters, at which to split,
 i.e. the delimiters).

 The split-function regards its first argument (a string) as a list of tokens
 separated by delimiters and it will store the list of tokens within the
 array-reference you have supplied. Note, that the array, which is passed as a
 reference (w$() in the synopsis), will be resized accordingly, so that you
 don't have to figure out the number of tokens in advance. The element at
 position zero (i.e. w$(0)) will not be used.

 normally (i.e. if you omit the third, which is the delimiter-argument) the
 function will regard space or tab as delimiters for tokens; however by
 supplying a third argument, you may split at any single of the characters
 within this string. E.g. if you supply ":;" as the third argument, then colon
 (:) or semicolon (;) will delimit tokens.

 Note, that a sequence of separator-characters will produce a sequence of empty
 tokens; that way, the number of tokens returned will always be one plus the
 number of separator characters contained within the string. Refer to the
 closely related token-function, if you do not like this behaviour. In some way,
 the split-function focuses on the separators (other than the token-function,
 which focuses on the tokens), hence its name.

 The second argument is a reference on a string-array, where the tokens will be
 stored; this array will be expanded (or shrunk) to have room for all tokens, if
 necessary.

 The first argument finally contains the text, that will be split into tokens.
 The split-function returns the number of tokens that have been found.

 Please see the examples below for some hints on the exact behaviour of the
 split-function and how it differs from the token-function:

 Example

 print "This program will help you to understand, how the"
 print "split()-function exactly works and how it behaves"
 print "in certain special cases."
 print
 print "Please enter a line containing tokens separated"
 print "by either '=' or '-'"
 dim t$(10)
 do
   print
   input "Please enter a line: " l$
   num=split(l$,t$(),"=-")
   print num," Tokens: ";
   for a=1 to num
     if (t$(a)="") then
       print "(EMPTY)";
     else
       print t$(a);
     endif
     if (a<num) print ",";
   next a
   print
 loop

 This program prints the following output:

 Please enter a line: a
 1 Tokens: a

 Please enter a line:
 0 Tokens:

 Please enter a line: ab
 1 Tokens: ab

 Please enter a line: a=b
 2 Tokens: a,b

 Please enter a line: a-
 2 Tokens: a,(EMPTY)

 Please enter a line: a-=
 3 Tokens: a,(EMPTY),(EMPTY)

 Please enter a line: =a-
 3 Tokens: (EMPTY),a,(EMPTY)

 Please enter a line: a=-b
 3 Tokens: a,(EMPTY),b

 Please enter a line: a--b-
 4 Tokens: a,(EMPTY),b,(EMPTY)

 Please enter a line: -a==b-c==
 7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)

 See also

 token

 -------------------------------------------------------------------------------

 Name

 sqr() ? compute the square of its argument

 Synopsis

 a=sqr(b)

 Description

 The sqr-function computes the square of its numerical argument (i.e. it
 multiplies its argument with itself).

 Example

 for a=1 to 10
   print a,sqr(a),a**2
 next a

 As you may see from the output, sqr can be written as **2 (or ^2) too.

 See also

 sqrt, **, ^

 -------------------------------------------------------------------------------

 Name

 sqrt() ? compute the square root of its argument

 Synopsis

 to be written

 Description

 The sqrt-function computes the square root of its numerical argument.

 Example

 for a=1 to 5
   print a,sqrt(a),a**(1/2)
 next a

 As you may see from the output, sqrt can be written as **(1/2) (or ^(1/2)) too.

 See also

 sqr, **, ^

 -------------------------------------------------------------------------------

 Name

 static ? preserves the value of a variable between calls to a subroutine

 Synopsis

 sub foo()

   static a

   ?

 end sub

 Description

 The static keyword can be used within subroutines to mark variables as static.
 This has two effects: First, the variable is local to the subroutine, i.e. its
 value is not know outside the subroutine (this is the effect of the local
 keyword). Second, the static-keyword arranges things, so that the variable
 keeps its value between invocations of the subroutine (this is different from
 the local-keyword).

 Example

 foo()
 foo()
 foo()

 sub foo()
   static a
   local b
   a=a+1
   b=b+1
   print a,b
 end sub

 This program shows the difference between static and local variables within a
 subroutine; it produces this output:

 1 1
 2 1
 3 1

 The output shows, that the static variable a keeps its value between subroutine
 calls, whereas b is initialized with the value 0 at every call to the
 subroutine foo.

 See also

 sub, local

 -------------------------------------------------------------------------------

 Name

 step ? specifies the increment step in a for-loop

 Synopsis

 for a=1 to 10 step 3
   ?
 next a

 Description

 Specify, by which amount the loop-variable of a for-loop will be incremented at
 each step.

 The step (as well as the lower and upper bound) are computed anew in each step;
 this is not common, but possible, as the example below demonstrates.

 Example

 for x=1 to 1000 step y
   y=x+y
   print x," ",y," ";
 next x
 print

 This program computes the fibonacci numbers between 1 and 1000.

 See also

 for

 -------------------------------------------------------------------------------

 Name

 str$() ? convert a number into a string

 Synopsis

 a$=str$(a)
 b$=str$(x,"##.###")
 b$=str$(x,"###,###.##")
 b$=str$(x,"###,###.##","_.")

 Description

 The str$-function accepts a numeric argument and returns it as a string. This
 conversion between number and string can be controlled with the optional third
 argument (the format argument). See the following table of examples to learn
 about valid values of this argument. Note, that those examples fall in one of
 two categories: C-style and basic-style; the first 4 examples in the table
 below are C-style, the rest of the examples are basic-style. For more
 information on the C-style formats, you may refer to your favorite
 documentation on the C programming language. The basic-style formats are much
 simpler, they just depict the desired output, marking digits with '#'; groups
 of (usually three) digits may be separated with colons (','), the decimal dot
 must be marked by a literal dot ('.'). Moreover these characters (colons and
 dot) may be replaced by other characters to satisfy the needs of non-english
 (e.g. german) languages; see the examples below.

 Note, that for clarity, each space in the result has been replaced by the
 letter 'x', because it would be hard to figure out, how many spaces are
 produced exactly otherwise.

 Table 7.2. Examples for the format argument

 +-----------------------------------------------------------------------------+
 |   Example   | Result for |                                                  |
 |   string    | converting |                   Description                    |
 |             |  1000*pi   |                                                  |
 |-------------+------------+--------------------------------------------------|
 |             |            |The '2' determines the minimum length of the      |
 |%2.5f        |3141.59265  |output; but if needed (as in the example) the     |
 |             |            |output can be longer. The '5' is the number of    |
 |             |            |digits after the decimal point.                   |
 |-------------+------------+--------------------------------------------------|
 |             |            |Two spaces (which appear as 'x') are added to pad |
 |%12.5f       |xx3141.59265|the output to the requested length of 12          |
 |             |            |characters.                                       |
 |-------------+------------+--------------------------------------------------|
 |             |            |The 'g' requests, that the precision ('5')        |
 |%012.5g      |0000003141.6|specifies the overall number of digits (before and|
 |             |            |after the decimal point).                         |
 |-------------+------------+--------------------------------------------------|
 |             |            |The '-' requests the output to be left-centered   |
 |%-12.5f      |3141.59265xx|(therefore the filling space appears at the       |
 |             |            |right).                                           |
 |-------------+------------+--------------------------------------------------|
 |             |            |Each '#' specifies a digit (either before or after|
 |             |            |the dot), the '.' specifies the position of the   |
 |#####.##     |x3141.59    |dot. As 1000*pi does not have enough digits, the 5|
 |             |            |requested digits before the dot are filled up with|
 |             |            |a space (which shows up as an 'x').               |
 |-------------+------------+--------------------------------------------------|
 |##,###.##    |x3,141.59   |Nearly the same as above, but the colon from the  |
 |             |            |format shows up within the result.                |
 |-------------+------------+--------------------------------------------------|
 |##,###.## and|            |                                                  |
 |an additional|x3.141,59   |Similar to the example above, but colon and dot   |
 |argument of  |            |are replaced with dot and colon respectively.     |
 |".,"         |            |                                                  |
 |-------------+------------+--------------------------------------------------|
 |##,###.## and|            |Similar to the example above, but colon and dot   |
 |an additional|x3_141,59   |are replaced with underscore and colon            |
 |argument of  |            |respectively.                                     |
 |"_,"         |            |                                                  |
 |-------------+------------+--------------------------------------------------|
 |             |            |The format string does not contain a dot, and     |
 |#####        |x3142       |therefore the result does not have any fractional |
 |             |            |digits.                                           |
 |-------------+------------+--------------------------------------------------|
 |             |            |As 1000*pi has 4 digits in front of the decimal   |
 |##.###       |##.###      |dot and the format only specifies 2, yabasic does |
 |             |            |not know what to do; therefore it chooses just to |
 |             |            |reproduce the format string.                      |
 +-----------------------------------------------------------------------------+

 Example

 do
   input "Please enter a format string: " f$
   a$=str$(1000*pi,f$)
   for a=1 to len(a$)
     if (mid$(a$,a,1)=" ") mid$(a$,a,1)="x"
   next a
   print a$
 loop

 This is the program, that has been used to get the results shown in the table
 above.

 See also

 print, using

 -------------------------------------------------------------------------------

 Name

 sub ? declare a user defined subroutine

 Synopsis

 foo(2,"hello")

 ?

 sub foo(bar,baz$)
   ?
   return qux
   ?
 end sub

 Description

 The sub-keyword starts the definition of a user defined subroutine. With user
 defined subroutines you are able to somewhat extend yabasic with your own
 commands or functions. A subroutine accepts arguments (numbers or strings) and
 returns a number or a string (however, you are not required to assign the value
 returned to a variable).

 The name of the subroutine follows after the keyword sub. If the name (in the
 synopsis: foo) ends on a '$', the subroutine should return a string (with the
 return-statement), otherwise a number.

 After the name of the subroutine yabasic requires a pair of braces; within
 those braces you may specify a list of parameters, for which values can (but
 need not) be included when calling the subroutine. If you omit one of those
 parameters when calling such a subroutine, it assumes the value zero (for
 numeric parameters) or the empty string (for string-parameters). However from
 the special variable numparams you may find out, how many arguments have really
 been passed when calling the subroutine.

 Parameters of a subroutine are always local variables (see the keyword local
 for more explanation).

 From within the subroutine you may return any time with the keyword return;
 along with the return-keyword you may specify the return value. Note that more
 than one return is allowed within a single subroutine.

 Finally, the keyword end sub ends the subroutine definition. Note, that the
 definition of a subroutine need not appear within the program before the first
 call to this sub.

 Note

 As braces have two uses in yabasic (i.e. for supplying arguments to a
 subroutine as well as to list the indices of an array). yabasic can not tell
 apart an array from a subroutine with the same name. Therefore you cannot
 define a subroutine with the same name as an array !

 Example

 p=2
 do
   if (is_prime(p)) print p
   p=p+1
 loop

 sub is_prime(a)
   local b
   for b=2 to sqrt(a)
     if (frac(a/b)=0) return false
   next b
   return true
 end sub

 This example is not the recommended way to compute prime numbers. However it
 gives a nice demonstration of using a subroutine.

 See also

 local, static, peek

 -------------------------------------------------------------------------------

 Name

 switch ? select one of many alternatives depending on a value

 Synopsis

 switch a
   case 1
   case 2
   ?
 end switch

 ?

 switch a$
   case "a"
   case "b"
 end switch

 Description

 The switch-statement selects one of many codepaths depending on a numerical or
 string expression. I.e. it takes an expression (either numeric or string) and
 compares it with a series of values, each wrapped within a case-clause. If the
 expression equals the value given in a case-clause, the subsequent statements
 are executed.

 The default-clause allows one to specify commands, which should be executed, if
 none of case-clauses matches.

 Note, that many case-clauses might be clustered (e.g. case "a":case "b":case
 "c"). Or put another way: You need a break-statement at the end of a
 case-branch, if you do not want to run into the next case.

 Example

 input "Please enter a single digit: " n
 switch n
   case 0:print "zero":break
   case 1:print "one":break
   case 2:print "two":break
   case 3:print "three":break
   case 4:print "four":break
   case 5:case 6: case 7:case 8:case 9
     print "Much !":break
   default:print "Hey ! That was more than a single digit !"
 end switch

 This example translates a single digit into a string; note, how the cases 5 to
 7 are clustered.

 See also

 switch, case, break

 -------------------------------------------------------------------------------

 Name

 system() ? hand a statement over to your operating system and return its
 exitcode

 Synopsis

 ret=system("foo")
 system("bar")

 Description

 The system-command accepts a single string argument, which specifies a command
 to be executed. The function will return the exitcode of the command; its
 output (if any) will be lost.

 Example

 print "Please enter the name of the file, that should be deleted."
 input f$
 if (system("rm "+f$+" >/dev/null 2>&1")) then
   print "Error !"
 else
   print "okay."
 endif

 This program is Unix-specific: It uses the Unix-command rm to remove a file.

 See also

 system$

 -------------------------------------------------------------------------------

 Name

 system$() ? hand a statement over to your operating system and return its
 output

 Synopsis

 print system$("dir")

 Description

 The system$-command accepts a single string argument, specifying a command,
 that can be found and executed by your operating system. It returns the output
 of this command as one big string.

 Example

 input "Please enter the name of a directory: " d$
 print
 print "This is the contents of the '"+d$+"':"
 print system$("dir "+d$)

 This example lists the contents of a directory, employing the dir-command
 (which is about the only program, that is known under Unix as well as Windows).

 See also

 system, chomp

 T

 tan() ? return the tangent of its argument
 tell ? get the current position within an open file
 text ? write text into your graphic-window
 then ? tell the long from the short form of the if-statement
 time$ ? return a string containing the current time
 to ? this keyword appears as part of other statements
 token() ? split a string into multiple strings
 triangle ? draw a triangle
 trim$() ? remove leading and trailing spaces from its argument
 true ? a constant with the value of 1

 Name

 tan() ? return the tangent of its argument

 Synopsis

 foo=tan(bar)

 Description

 The tan-function computes the tangent of its arguments (which should be
 specified in radians).

 Example

 for a=0 to 45
   print tan(a*pi/180)
 next a

 This example simply prints the tangent of all angles between 0 and 45 degrees.

 See also

 atan, sin

 -------------------------------------------------------------------------------

 Name

 tell ? get the current position within an open file

 Synopsis

 open #1,"foo"
   ?
 position=tell(#1)

 Description

 The tell-function requires the number of an open file as an argument. It
 returns the position (counted in bytes, starting from the beginning of the
 file) where the next read will start.

 Example

 open #1,"foo","w"
 print #1 "Hello World !"
 close #1

 open #1,"foo"
 seek #1,0,"end"
 print tell(#1)
 close 1

 This example (mis)uses tell to get the size of the file. The seek positions the
 file pointer at the end of the file, therefore the call to tell returns the
 total length of the file.

 See also

 tell, open

 -------------------------------------------------------------------------------

 Name

 text ? write text into your graphic-window

 Synopsis

 text x,y,"foo"
 text x,y,"foo","lb"
 text x,y,"foo","cc","font"
 text x,y,"foo","font","rt"

 Description

 The text-commands displays a text-string (the third argument) at the given
 position (the first two arguments) within an already opened window. The font to
 be used can be optionally specified as either the fourth or fifth argument
 ("font" in the example above). A font specified this way will also be used for
 any subsequent text-commands, as long as they do not specify a font themselves.

 The fourth or fifth optional argument ("lb" in the example above) can be used
 to specify the alignment of the text with respect to the specified position.
 This argument is always two characters long: The first character specifies the
 horizontal alignment and can be either l, r or c, which stand for left, right
 or center. The second character specifies the vertical alignment and can be one
 of t, b or c, which stand for top, bottom or center respectively. If you omit
 this alignment argument, the default "lb" applies; however this default may be
 changed with poke "textalign","xx"

 Example

 open window 500,200
 clear screen
 data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
 for a=1 to 9
   read align$
   print "Alignment: ",align$
   line 50*a-15,100,50*a+15,100
   line 50*a,85,50*a,115
   text 50*a,100,"Test",align$
   inkey$
 next a

 This program draws nine crosses and writes the same text at each; however it
 goes through all possible nine alignment strings, showing their effect.

 See also

 open window, peek, poke

 -------------------------------------------------------------------------------

 Name

 then ? tell the long from the short form of the if-statement

 Synopsis

 if (a<b) then
   ?
 endif

 Description

 The keyword then is part of the if-statement; please see there for further
 explanations. However, not every if-statement requires the keyword then: If the
 keyword then is present, the if-clause may extend over more than one line, and
 the keyword endif is required to end it. If the keyword then is not present,
 the if-statement extends up to the end of the line, and any endif would be an
 error.

 Example

 if (1<2) then
   print "Hello ";
 endif

 if (2<3) print "world"
 if (2<1)
   print "!"

 This example prints Hello world. Note, that no exclamation mark (!) is printed,
 which might come as a surprise and may be changed in future versions of yabasic
 .

 See also

 if

 -------------------------------------------------------------------------------

 Name

 time$ ? return a string containing the current time

 Synopsis

 print time$
 print time$()

 Description

 The time$ function returns the current time in four fields separated by hyphens
 '-'. The fields are:

   * The current hour in the range from 0 to 23, padded with zeroes (e.g. 00 or
     04) to a length of two characters.

   * The number of minutes, padded with zeroes.

   * The number of seconds, padded with zeroes.

   * The number of seconds, that have elapsed since the program has been
     started. This value increases as long as your program runs and is therefore
     unbound and not padded with zeroes.

 At the time of writing this documentation, time$ returns 22-58-53-0. Note, that
 the first three of the four fields returned by time$ have a fixed width;
 therefore it is easy to extract some fields with the usual string-functions
 mid$ (and others).

 Example

 print "Hello it is ",time$
 print "An empty for-loop with ten million iterations takes ";
 for a=1 to 10000000:next a
 print "Now it is ",time$
 print peek("secondsrunning")," seconds have passed."

 This program benchmarks the for-loop; however, it does not use the fourth field
 of the string returned by time$, because that string wraps around every 60
 seconds; rather the peek "secondsrunning" is queried.

 See also

 date

 -------------------------------------------------------------------------------

 Name

 to ? this keyword appears as part of other statements

 Synopsis

 for a=1 to 100 step 2
   ?
 next a

 line x,y to a,b

 Description

 The to-keyword serves two purposes (which are not related at all):

   * within for-statements, to specify the upper bound of the loop.

   * Within any graphical command (e.g. line), that requires two points (i.e.
     four numbers) as arguments, a comma ',' might be replaced with the keyword
     to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200 in
     such commands.

 Example

 Please see the command listed under "See also" for examples.

 See also

 for, line, rectangle

 -------------------------------------------------------------------------------

 Name

 token() ? split a string into multiple strings

 Synopsis

 dim w$(10)
 ?
 num=token(a$,w$())
 num=token(a$,w$(),s$)

 Description

 The token-function accepts a string (containing the text to be split), a
 reference to a string-array (which will receive the resulting strings, i.e. the
 tokens) and an optional string (with a set of characters, at which to split,
 i.e. the delimiters).

 The token-function regards its first argument as a list of tokens separated by
 delimiters and it will store the list of tokens within the array-reference that
 has been supplied. Note, that the array, which is passed as a reference (w$()
 in the synopsis), will be resized accordingly, so that you don't have to figure
 out the number of tokens in advance. The element at position zero (i.e. w$(0))
 will not be used.

 Normally (i.e. if you omit the third, the delimiter-argument) the function will
 regard space or tab as delimiters for tokens; however by supplying a third
 argument, you may split at any single of the characters within this string.
 E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;)
 will delimit tokens.

 Note, that token will never produce empty tokens, even if two or more
 separators follow in sequence. Refer to the closely related split-function, if
 you do not like this behaviour. In some way, the token-function focuses on the
 tokens and not on the separators (other than the split-function, which focuses
 on the separators).

 The second argument is a reference on a string-array, where the tokens will be
 stored; this array will be expanded (or shrunk) as necessary to have room for
 all tokens.

 The first argument finally contains the text, that will be split into tokens.
 The token-function returns the number of tokens, that have been found.

 Please see the examples below for some hints on the exact behaviour of the
 token-function and how it differs from the split-function:

 Example

 print "This program will help you to understand, how the"
 print "token()-function exactly works and how it behaves"
 print "in certain special cases."
 print
 print "Please enter a line containing tokens separated"
 print "by either '=' or '-'"
 dim t$(10)
 do
   print
   input "Please enter a line: " l$
   num=token(l$,t$(),"=-")
   print num," Tokens: ";
   for a=1 to num
     if (t$(a)="") then
       print "(EMPTY)";
     else
       print t$(a);
     endif
     if (a<num) print ",";
   next a
   print
 loop

 This program prints the following output:

 Please enter a line: a
 1 Tokens: a

 Please enter a line:
 0 Tokens:

 Please enter a line: ab
 1 Tokens: ab

 Please enter a line: a=b
 2 Tokens: a,b

 Please enter a line: a-
 1 Tokens: a

 Please enter a line: a-=
 1 Tokens: a

 Please enter a line: =a-
 1 Tokens: a

 Please enter a line: a=-b
 2 Tokens: a,b

 Please enter a line: a--b-
 2 Tokens: a,b

 Please enter a line: -a==b-c==
 3 Tokens: a,b,c

 See also

 split

 -------------------------------------------------------------------------------

 Name

 triangle ? draw a triangle

 Synopsis

 open window 100,100
 triangle 100,100,50,50,100,50
 fill triangle 50,100,100,50,200,200
 clear fill triangle 20,20,10,10,200,200

 Description

 The triangle-command draws a triangle; it requires 6 parameters: The x- and
 y-coordinates of the three points making up the triangle. With the optional
 keywords clear and fill (which may appear both and in any sequence) the
 triangle can be cleared and filled respectively.

 Example

 open window 200,200
 do
   phi=phi+0.2
   i=i+2
   color mod(i,255),mod(85+2*i,255),mod(170+3*i,255)
   dx=100*sin(phi):dy=20*cos(phi)
   fill triangle 100+20*sin(phi),100+20*cos(phi),100-20*sin(phi),100-20*cos(phi),100-80*cos(phi),100+80*sin(phi)
   sleep 0.1
 loop

 This example draws a colored triangles until you get exhausted.

 See also

 open window, open printer, line, circle, rectangle

 -------------------------------------------------------------------------------

 Name

 trim$() ? remove leading and trailing spaces from its argument

 Synopsis

 a$=trim$(b$)

 Description

 The trim$-function removes all whitespace from the left and from the right end
 of a string and returns the result. Calling trim$ is equivalent to calling
 rtrim$(ltrim$()).

 Example

 do
   input "Continue ? Please answer yes or no: " a$
   a$=lower$(trim$(a$))
   if (len(a$)>0 and a$=left$("no",len(a$)) exit
 loop

 This example asks for an answer (yes or no) and removes spaces with trim$ to
 make the comparison with the string "no" more bulletproof.

 See also

 ltrim$, rtrim$

 -------------------------------------------------------------------------------

 Name

 true ? a constant with the value of 1

 Synopsis

 okay=true

 Description

 The constant true can be assigned to variables which will later appear in
 conditions (e.g. an if-statement.

 true may also be written as TRUE or even TrUe.

 Example

 input "Please enter a string of all upper letters: " a$
 if (is_upper(a$)) print "Okay"

 sub is_upper(a$)
   if (a$=upper$(a$)) return true
   return false
 end sub

 See also

 false

 U

 until ? end a repeat-loop
 upper$() ? convert a string to upper case
 using ? Specify the format for printing a number

 Name

 until ? end a repeat-loop

 Synopsis

 repeat
   ?
 until (?)

 Description

 The until-keyword ends a loop, which has been introduced by the repeat-keyword.
 until requires a condition in braces (or an expression, see here for details)
 as an argument; the loop will continue until this condition evaluates to true.

 Example

 c=1
 s=1
 repeat
   l=c
   s=-(s+sig(s))
   c=c+1/s
   print c
 until(abs(l-c)<0.000001)

 This program calculates the sequence 1/1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+ ? ;
 please let me know, if you know against which value this converges.

 See also

 repeat

 -------------------------------------------------------------------------------

 Name

 upper$() ? convert a string to upper case

 Synopsis

 u$=upper$(a$)

 Description

 The upper$-function accepts a single string argument and converts it to all
 upper case.

 Example

 line input "Please enter a sentence without the letter 'e': " l$
 p=instr(upper$(l$),"E")
 if (p) then
   l$=lower$(l$)
   mid$(l$,p,1)="E"
   print "Hey, you are wrong, see here!"
   print l$
 else
   print "Thanks."
 endif

 This program asks for a sentence and marks the first (if any) occurrence of the
 letter 'e' by converting it to upper case (in contrast to the rest of the
 sentence, which is converted to lower case).

 See also

 lower$

 -------------------------------------------------------------------------------

 Name

 using ? Specify the format for printing a number

 Synopsis

 print a using "##.###"
 print a using("##.###",",.")

 Description

 The using-keyword may appear as part of the print-statement and specifies the
 format (e.g. the number of digits before and after the decimal dot), which
 should be used to print the number.

 The possible values for the format argument ("##.###" in the synopsis above)
 are described within the entry for the str$-function; especially the second
 line in the synopsis (print a using("##.###",",.")) will become clear after
 referring to str$. In fact the using clause is closely related to the
 str$-function; the former can always be rewritten using the latter; i.e. print
 foo using bar$ is always equivalent to print str$(foo,bar$). Therefore you
 should check out str$ to learn more.

 Example

 for a=1 to 10
   print sqrt(ran(10000*a)) using "#########.#####"
 next a

 This example prints a column of square roots of random number, nicely aligned
 at the decimal dot.

 See also

 print, str$

 V

 val() ? converts a string to a number

 Name

 val() ? converts a string to a number

 Synopsis

 x=val(x$)

 Description

 The val-function checks, if the start of its string argument forms a floating
 point number and then returns this number. The string therefore has to start
 with digits (only whitespace in front is allowed), otherwise the val-function
 returns zero.

 Example

 input "Please enter a length, either in inches (in) or centimeters (cm) " l$
 if (right$(l$,2)="in") then
   l=val(l$)*2.51
 else
   l=val(l$)
 print "You have entered ",l,"cm."

 This example queries for a length and checks, if it has been specified in
 inches or centimeters. The length is then converted to centimeters.

 See also

 str$

 W

 wait ? pause, sleep, wait for the specified number of seconds
 wend ? end a while-loop
 while ? start a while-loop
 window origin ? move the origin of a window

 Name

 wait ? pause, sleep, wait for the specified number of seconds

 Synopsis

 wait 4

 Description

 The wait-command has many different names: You may write pause, sleep or wait
 interchangeably; whatever you write, yabasic will always do exactly the same.

 Therefore you should refer to the entry for the pause-function for further
 information.

 -------------------------------------------------------------------------------

 Name

 wend ? end a while-loop

 Synopsis

 while(a<b)
   ?
 wend

 Description

 The wend-keyword marks the end of a while-loop. Please see the while-keyword
 for more details.

 wend can be written as end while or even end-while.

 Example

 line input "Please enter a sentence: " a$
 p=instr(a$,"e")
 while(p)
   mid$(a$,p,1)="E"
   p=instr(a$,"e")
 wend
 print a$

 This example reads a sentence and converts every occurrence of the letter e
 into uppercase (E).

 See also

 while (which is just the following entry).

 -------------------------------------------------------------------------------

 Name

 while ? start a while-loop

 Synopsis

 while(?)
   ?
 wend

 Description

 The while-keyword starts a while-loop, i.e. a loop that is executed as long as
 the condition (which is specified in braces after the keyword while) evaluates
 to true.

 Note, that the body of such a while-loop will not be executed at all, if the
 condition following the while-keyword is not true initially.

 If you want to leave the loop prematurely, you may use the break-statement.

 Example

 open #1,"foo"
 while(!eof(1))
   line input #1 a$
   print a$
 wend

 This program reads the file foo and prints it line by line.

 See also

 until, break, wend, do

 -------------------------------------------------------------------------------

 Name

 origin ? move the origin of a window

 Synopsis

 open window 200,200
 origin "cc"

 Description

 The origin-command applies to graphic windows and moves the origin of the
 coordinate system to one of nine point within the window. The normal position
 of the origin is in the upper left corner of the window; however in some cases
 this is inconvenient and moving the origin may save you from subtracting a
 constant offset from all of your coordinates.

 However, you may not move the origin to an arbitrary position; in horizontal
 position there are only three positions: left, center and right, which are
 decoded by the letters l, c and r. In vertical position the allowed positions
 are top, center and bottom; encoded by the letters t, c and b. Taking the
 letters together, you arrive at a string, which might be passed as an argument
 to the command; e.g. "cc" or "rt".

 Example

 100,100

 open window 200,200
 window origin "cc"
 circle 0,0,60

 This example draws a circle, centered at the center of the window.

 See also

 open window

 X

 xor() ? compute the exclusive or

 Name

 xor() ? compute the exclusive or

 Synopsis

 x=xor(a,b)

 Description

 The xor computes the bitwise exclusive or of its two numeric arguments. To
 understand the result, both arguments should be viewed as binary numbers (i.e.
 a series of 0 and 1); a bit of the result will then be 1, if exactly one
 argument has a 1 and the other has a 0 at this position in their binary
 representation.

 Note, that both arguments are silently converted to integer values and that
 negative numbers have their own binary representation and may lead to
 unexpected results when passed to and.

 Example

 print xor(7,4)

 This will print 3. This result is obvious, if you note, that the binary
 representation of 7 and 4 are 111 and 100 respectively; this will yield 011 in
 binary representation or 2 as decimal.

 The eor-function is the same as the xor function; both are synonymous; however
 they have each their own description, so you may check out the entry of eor for
 a slightly different view.

 See also

 and, or, eor, not

 Special characters

 # ? either a comment or a marker for a file-number
 // ? starts a comment
 @ ? synonymous to at
 : ? separate commands from each other
 ; ? suppress the implicit newline after a print-statement
 ** or ^ ? raise its first argument to the power of its second

 Name

 # ? either a comment or a marker for a file-number

 Synopsis

 # This is a comment, but the line below not !
 open #1,"foo"

 Description

 The hash ('#') has two totally unrelated uses:

   * A hash might appear in commands related with file-io. yabasic uses simple
     numbers to refer to open files (within input, print, peek or eof). In those
     commands the hash may precede the number, which species the file. Please
     see those commands for further information and examples; the rest of this
     entry is about the second use (as a comment).

   * As the very first character within a line, a hash introduces comments
     (similar to rem).

 '#' as a comment is common in most scripting languages and has a special use
 under Unix: If the very first line of any Unix-program begins with the
 character sequence '#!' ("she-bang", no spaces allowed), the rest of the line
 is taken as the program that should be used to execute the script. I.e. if your
 yabasic-program starts with '#!/usr/local/bin/yabasic', the program /usr/local/
 bin/yabasic will be invoked to execute the rest of the program. As a remark for
 windows-users: This mechanism ensures, that yabasic will be invoked to execute
 your program; the ending of the file (e.g. .yab) will be ignored by Unix.

 Example

 # This line is a valid comment
 print "Hello " : # But this is a syntax error, because
 print "World!" : # the hash is not the first character !

 Note, that this example will produce a syntax error and is not a valid program
 !

 See also

 input, print, peek or eof, //, rem

 -------------------------------------------------------------------------------

 Name

 // ? starts a comment

 Synopsis

 //  This is a comment !

 Description

 The double-slash ('//') is (besides REM and '#') the third way to start a
 comment. '//' is the latest and greatest in the field of commenting and allows
 yabasic to catch up with such cool languages like C++ and Java.

 Example

 // Another comment.
 print "Hello world !" // Another comment

 Unlike the example given for '#' this example is syntactically correct and will
 not produce an error.

 See also

 #, rem

 -------------------------------------------------------------------------------

 Name

 @ ? synonymous to at

 Synopsis

 clear screen
 ?
 print @(a,b)

 Description

 As '@' is simply a synonym for at, please see at for further information.

 See also

 at

 -------------------------------------------------------------------------------

 Name

 : ? separate commands from each other

 Synopsis

 print "Hello ":print "World"

 Description

 The colon (':') separates multiple commands on a single line.

 The colon and the newline-character have mostly the same effect, only that the
 latter, well, starts a new line too. The only other difference is their effect
 within the (so-called) short if, which is an if-statement without the keyword
 then. Please see the entry for if for more details.

 Example

 if (a<10) print "Hello ":print "World !"

 This example demonstrates the difference between colon and newline as described
 above.

 See also

 if

 -------------------------------------------------------------------------------

 Name

 ; ? suppress the implicit newline after a print-statement

 Synopsis

 print "foo",bar;

 Description

 The semicolon (';') may only appear at the last position within a print
 -statement. It suppresses the implicit newline, which yabasic normally adds
 after each print-statement.

 Put another way: Normally the output of each print-statement appears on a line
 by itself. If you rather want the output of many print-statements to appear on
 a single line, you should end the print-statement with a semicolon.

 Example

 print "Hello ";:print "World !"

 This example prints Hello World ! in a single line.

 See also

 print

 -------------------------------------------------------------------------------

 Name

 ** or ^ ? raise its first argument to the power of its second

 Synopsis

 print 2**b
 print 3^4

 Description

 ** (or ^, which is an exact synonym), is the arithmetic operator of
 exponentiation; it requires one number to its left and a second one to its
 right; ** then raises the first argument to the power of the second and returns
 the result. The result will only be computed if it yields a real number (as
 opposed to a complex number); this means, that the power can not be computed,
 if the first argument is negative and the second one is fractional. On the
 other hand, the second argument can be fractional, if the first one ist
 positive; this means, that ** may be used to compute arbitrary roots: e.g.
 x**0.5 computes the square root of x.

 Example

 print 2**0.5

 See also

 sqrt

 Reserved Words

 Here is a list of all reserved words in yabasic. Please make sure, that you do
 not try to use one of them as the name of a variable or subroutine. Or, the
 other way around: If you get some mysterious error from yabasic and you just
 can't figure out why, then you might be using one of the reserved words below,
 without knowing.

 Anyway, here is the list:

 ABS       ACOS          AND      ARRAYDIM   ARRAYDIMENSION
 ARRAYSIZE AS            ASC      ASIN       AT
 ATAN      BEEP          BELL     BIN$       BIND
 BITBLIT   BITBLIT$      BITBLT   BITBLT$    BOX
 BREAK     CASE          CHR$     CIRCLE     CLEAR
 CLOSE     COLOR         COLOUR   COMPILE    CONTINUE
 COS       CURVE         DATA     DATE$      DEC
 DEFAULT   DIM           DO       DOT        ELSE
 ELSEIF    ELSIF         END      ENDIF      EOF
 EOR       ERROR         EXECUTE  EXECUTE$   EXIT
 EXP       EXPORT        FI       FILL       FILLED
 FOR       FRAC          GETBIT$  GETSCREEN$ GLOB
 GOSUB     GOTO          HEX$     IF         INKEY$
 INPUT     INSTR         INT      INTERRUPT  LABEL
 LEFT$     LEN           LET      LINE       LOCAL
 LOG       LOOP          LOWER$   LTRIM$     MAX
 MID$      MIN           MOD      MOUSEB     MOUSEBUTTON
 MOUSEMOD  MOUSEMODIFIER MOUSEX   MOUSEY     NEW
 NEXT      NOT           NUMPARAM ON         OPEN
 OR        ORIGIN        PAUSE    PEEK       PEEK$
 POKE      PRINT         PRINTER  PUTBIT     PUTSCREEN
 RAN       READ          READING  RECT       RECTANGLE
 REDIM     REPEAT        RESTORE  RETURN     REVERSE
 RIGHT$    RINSTR        RTRIM$   SCREEN     SEEK
 SIG       SIN           SLEEP    SPLIT      SPLIT$
 SQR       SQRT          STATIC   STEP       STR$
 SUB       SUBROUTINE    SWITCH   SYSTEM     SYSTEM$
 TAN       TELL          TEXT     THEN       TIME$
 TO        TOKEN         TOKEN$   TRIANGLE   TRIM$
 UNTIL     UPPER$        USING    VAL        WAIT
 WEND      WHILE         WINDOW   WRITING    XOR

 Please see here for explanations on how to use these words in yabasic.

 Chapter 8. Some general concepts and terms

 Logical shortcuts
 Conditions and expressions
 References on arrays
 Specifying Filenames under Windows
 Escape-sequences
 Creating a standalone program from your yabasic-program

 This chapter presents some general concepts and terms, which deserve a
 description on their own, but are not associated with a single command or
 function in yabasic. Most of these topics do not lend themselves to be read
 alone, rather they might be read (or skimmed) as background material if an
 entry from the alphabetical list of commands refers to them.

 Logical shortcuts

 Logical shortcuts are no special language construct and there is no keyword for
 them; they are just a way to evaluate logical expressions. Logical expressions
 (i.e. a series of conditions or comparisons joined by and or or) are only
 evaluated until the final result of the expression can be determined. An
 example:

 if (a<>0 and b/a>2) print "b is at least twice as big as a"

 The logical expression a<>0 and b/a>2 consists of two comparisons, both of
 which must be true, if the print statement should be executed. Now, if the
 first comparison (a<>0) is false, the whole logical expression can never be
 true and the second comparison (b/a>2) need not be evaluated.

 This is exactly, how yabasic behaves: The evaluation of a composed logical
 expressions is terminated immediately, as soon as the final result can be
 deduced from the already evaluated parts.

 In practice, this has the following consequences:

   * If two or more comparisons are joined with and and one comparison results
     in false, the logical expression is evaluated no further and the overall
     result is false.

   * If two or more comparisons are joined with or and one comparison results in
     true, the logical expression is evaluated no further and the result is
     true.

 ?Nice, but whats this good for ??, I hear you say. Well, just have another look
 at the example, especially the second comparison (b/a>2); dividing b by a is
 potentially hazardous: If a equals zero, the expression will cause an error and
 your program will terminate. To avoid this, the first part of the comparison (a
 <>0) checks, if the second one can be evaluated without risk. This pre-checking
 is the most common usage and primary motivation for logical shortcuts (and the
 reason why most programming languages implement them).

 Conditions and expressions

 Well, bottomline there is no difference or distinction between conditions and
 expressions, at least as yabasic is concerned. So you may assign the result of
 comparisons to variables or use an arithmetic expression or a simple variable
 within a condition (e.g. within an if-statement). So the constructs shown in
 the example below are all totally valid:

 input "Please enter a number between 1 and 10: " a

 rem   Assigning the result of a comparison to a variable
 okay=a>=1 and a<=10

 rem   Use a variable within an if-statement
 if (not okay) error "Wrong, wrong !"

 So conditions and expressions are really the same thing (at least as long as
 yabasic is concerned). Therefore the terms conditions and expression can really
 be used interchangeably, at least in theory. In reality the term condition is
 used in connection with if or while whereas the term expression tends to be
 used more often within arithmetic context.

 References on arrays

 References on arrays are the only way to refer to an array as a whole and to
 pass it to subroutines or functions like arraydim or arraysize. Whereas (for
 example) a(2) designates the second element of the array a, a() (with empty
 braces) refers to the array a itself. a() is called an array reference.

 If you pass an array reference to one of your own subroutines, you need to be
 aware, that the subroutine will be able to modify the array you have passed in.
 So passing an array reference does not create a copy of the array; this has
 some interesting consequences:

   * Speed and space: Creating a copy of an array would be a time (and resource)
     consuming operation; passing just a reference is cheap and fast.

   * Returning many values: A subroutine, that wants to give back more than one
     value, may require an array reference among its arguments and then store
     its many return values within this array. This is the only way to return
     more than one value from a subroutine.

 Specifying Filenames under Windows

 As you probably know, windows uses the character '' to separate the
 directories within a pathname; an example would be C:yabasicyabasic.exe (the
 usual location of the yabasic executable). However, the very same character ''
 is used to construct escape sequences, not only in yabasic but in most other
 programming languages.

 Therefore the string "C:	.dat" does not specify the file t.dat within the
 directory C:; this is because the sequence '	' is translated into the
 tab-character. To specify this filename, you need to use the string "C:\t.dat"
 (note the double slash '\').

 Escape-sequences

 Escape-sequences are the preferred way of specifying 'special' characters. They
 are introduced by the ''-character and followed by one of a few regular
 letters, e.g. ' or '' (see the table below).

 Escape-sequences may occur within any string at any position; they are replaced
 at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the
 string, with their corresponding special character. As a consequence of this
 len("") returns 1, because yabasic replaces "" with the matching special
 character just before the program executes.

 Table 8.1. Escape sequences

 +--------------------------------------------+
 |Escape Sequence| Matching special character |
 |---------------+----------------------------|
 |            |newline                     |
 |---------------+----------------------------|
 |	             |tabulator                   |
 |---------------+----------------------------|
 |           |vertical tabulator          |
 |---------------+----------------------------|
 |           |backspace                   |
 |---------------+----------------------------|
 |             |carriage return             |
 |---------------+----------------------------|
 |            |formfeed                    |
 |---------------+----------------------------|
 |             |alert (i.e. a beeping sound)|
 |---------------+----------------------------|
 |\             |backslash                   |
 |---------------+----------------------------|
 |'             |single quote                |
 |---------------+----------------------------|
 |
 |---------------+----------------------------|
 |EX) (see below)       |
 +--------------------------------------------+

 Note, that an escape sequences of the form
 characters as long as you know their position (as a hex-number) within the
 ascii-charset: For example
 chr$(dec("12",16)). Note that a hexa-decimal number (and the
 hexa-decimal string "12" corresponds to the decimal number 18).

 Creating a standalone program from your yabasic-program

 Creating a standalone-program from the command line
 Creating a standalone-program from within your program
 Downsides of creating a standalone program
 See also

 Note

 The bind-feature, which is described below, is at an experimental stage right
 now. It works (at least for me !) under Windows and Linux, but I cannot even
 promise it for other variants of Unix. However, if it does not work for your
 Unix, I will at least try to make it work, if you give me sufficient
 information of your system.

 Sometimes you may want to give one of your yabasic-programs to other people.
 However, what if those other people do not have yabasic installed ? In that
 case you may create a standalone-program from your yabasic-program, i.e. an
 executable, that may be executed on its own, standalone, even (and especially
 !) on computers, that do not have yabasic installed. Having created a
 standalone program, you may pass it around like any other program (e.g. one
 written in C) and you can be sure that your program will execute right away.

 Such a standalone-program is simply created by copying the full yabasic
 -interpreter and your yabasic-program (plus all the libraries it does import)
 together into a single, new program, whose name might be chosen at will (under
 windows of course it should have the ending .exe). If you decide to create a
 standalone-program, there are three bits in yabasic, that you may use:

   * The bind-command, which does the actual job of creating the standalone
     program from the yabasic-interpreter and your program.

   * The command-line Option --bind (see options), which does the same from the
     command-line.

   * The special peek("isbound"), which may be used to check, if the yabasic
     -program containing this peek is bound to the interpreter as part of a
     standalone program.

 With these bits you know enough to create a standalone-program. Actually there
 are two ways to do this: on the command line and from within your program.

 Creating a standalone-program from the command line

 Let's say you have the following very simple program within the file foo.yab:

 print "Hello World !"

 Normally you would start this yabasic-program by typing yabasic foo.yab and as
 a result the string Hello World ! would appear on your screen. However, to
 create a standalone-program from foo.yab you would type:

 yabasic -bind foo.exe foo.yab

 This command does not execute your program foo.yab but rather create a
 standalone-program foo.exe. Note: under Unix you would probably name the
 standalone program foo or such, omitting the windows-specific ending .exe.

 Yabasic will confirm by printing something like: ---Info: Successfully bound
 'yabasic' and 'foo.yab' into 'foo.exe'.

 After that you will find a program foo.exe (which must be made executable with
 the chmod-command under Unix first). Now, executing this program foo.exe (or
 foo under Unix) will produce the output Hello World !.

 This newly created program foo.exe might be passed around to anyone, even if he
 does not have yabasic installed.

 Creating a standalone-program from within your program

 It is possible to write a yabasic-program, that binds itself to the yabasic
 -interpreter. Here is an example:

 if (!peek("isbound")) then
   bind "foo"
   print "Successfully created the standalone executable 'foo' !"
   exit
 endif

 print "Hello World !"

 If you run this program (which may be saved in the file foo.yab) via yabasic
 foo.yab, the peek("isbound") in the first line will check, if the program is
 already part of a standalone-program. If not (i.e. if the yabasic-interpreter
 and the yabasic-program are separate files) the bind-command will create a
 standalone program foo containing both. As a result you would see the output
 Successfully created the standalone executable 'foo' !. Note: Under Windows you
 would probably choose the filename foo.exe.

 Now, if you run this standalone executable foo (or foo.exe), the very same
 yabasic-program that is shown above will be executed again. However, this time
 the peek("isbound") will return TRUE and therefore the condition of the
 if-statement is false and the three lines after then are not executed. Rather
 the last print-statement will run, and you will see the output Hello World !.

 That way a yabasic-program may turn itself into a standalone-program.

 Downsides of creating a standalone program

 Now, before you go out and turn all your yabasic-programs into standalone
 programs, please take a second to consider the downsides of doing so:

   * The new standalone program will be at least as big as the interpreter
     itself, so you need to pass a few hundred kilobytes around, just to save
     people from having to install yabasic themselves.

   * There is no easy way to extract your yabasic-program from within the
     standalone program: If you ever want to change it, you need to have it
     around separately.

   * If a new version of yabasic becomes available, again you need to recreate
     all of your standalone programs to take advantage of bugfixes and
     improvements.

 So, being able to create a standalone program is certainly a good thing, but
 certainly not a silver bullet.

 See also

 The bind-command, the peek-function and the command line options.

 Chapter 9. A few example programs

 A very simple program
 The demo of yabasic

 A very simple program

 The program below is a very simple program:

 repeat
   input "Please enter the first number, to add " a
   input "Please enter the second number, to add " b
   print a+b
 until(a=0 and b=0)

 This program requests two numbers, which it than adds. The process is repeated
 until you enter zero (or nothing) twice.

 The demo of yabasic

 The listing below is the demo of yabasic. Note, that parts of this demo have
 been written before some of the more advanced features (e.g subroutines) of
 yabasic have been implemented. So please do not take this as a particular good
 example of yabasic-code.

 //
 //      This program demos yabasic
 //

 //      Check, if screen is large enough
 clear screen
 sw=peek("screenwidth"):sh=peek("screenheight")
 if (sw<78 or sh<24) then
   print
   print "  Sorry, but your screen is to small to run this demo !"
   print
   end
 endif
 sw=78:sh=24

 //  Initialize everything
 restore mmdata
 read mmnum:dim mmtext$(mmnum)
 for a=1 to mmnum:read mmtext$(a):next a

 //  Main loop selection of demo
 ysel=1
 label mainloop
 clear screen
 print colour("cyan","magenta") at(7,2) "################################"
 print colour("cyan","magenta") at(7,3) "################################"
 print colour("cyan","magenta") at(7,4) "################################"
 print colour("yellow","blue") at(8,3) " This is the demo for yabasic "
 yoff=7
 for a=1 to mmnum
   if (a=mmnum) then ydisp=1:else ydisp=0:fi
   if (a=ysel) then
     print colour("blue","green") at(5,yoff+ydisp+a) mmtext$(a);
   else
     print at(5,yoff+ydisp+a) mmtext$(a);
   endif
 next a
 print at(3,sh-3) "Move selection with CURSOR KEYS (or u and d),"
 print at(3,sh-2) "Press RETURN or SPACE to choose, ESC to quit."

 do    // loop for keys pressed
   rev=1
   do    // loop for blinking
     k$=inkey$(0.4)
     if (k$="") then
       if (ysel=mmnum) then
         if (rev=1) then
           print colour("blue","green") at(5,yoff+mmnum+1) mmtext$(mmnum);
           rev=0
         else
           print colour("yellow","red") at(5,yoff+mmnum+1) mmtext$(mmnum);
           rev=1
         endif
       endif
     else    // key has been pressed, leave loop
       break
     endif
   loop    // loop for blinking

   yalt=ysel
   if (k$="up" or k$="u") then
     if (ysel=1) then ysel=mmnum else ysel=ysel-1 fi
     redraw():heal():continue
   fi
   if (k$="down" or k$="d") then
     if (ysel=mmnum) then ysel=1 else ysel=ysel+1 fi
     redraw():heal():continue
   fi
   if (k$=" " or k$="enter" or k$="right") then
     on ysel gosub overview,bitmap,tetraeder,endit
     goto mainloop
   fi
   if (k$="esc") then
     endit()
   fi
   beep
   print at(3,sh-5) "Invalid key: ",k$,"         "
 loop    // loop for keys pressed

 //  redraw line
 sub redraw()
   if (yalt=mmnum) then ydisp=1:else ydisp=0:fi
   print at(5,yoff+yalt+ydisp) mmtext$(yalt);
   if (ysel=mmnum) then ydisp=1:else ydisp=0:fi
   print colour("blue","green") at(5,yoff+ysel+ydisp) mmtext$(ysel);
   return
 end sub

 //  erase a line
 sub heal()
   print at(3,sh-5) "                                                       "
   return
 end sub

 //  Go here to exit
 label endit
   print at(3,sh-8) "Hope you liked it ...  ";
   exit
 return

 //  Present a short overview
 label overview
   clear screen
   print
   print "  Yabasic is a quite traditional basic: It comes with"
   print "  print, input, for-next-loops, goto, gosub, while and"
   print "  repeat. It has user defined procedures and libraries,"
   print "  however, it is not object oriented.
   print "  Yabasic makes it easy to open a window, draw lines"
   print "  and print the resulting picture.
   print "  Yabasic programs are interpreted and run under Unix"
   print "  and Windows. The Yabasic interpreter (around 200K)"
   print "  and any Yabasic program can be glued together to"
   print "  form a standalone executable.
   print "  Yabasic is free software, i.e. subject to the"
   print "  MIT License.
   print "n While you read this, I am calculating prime numbers,
   print "  Press any key to return to main menu ..."
   can=1
   print at(6,17) "This is a prime number: "
   label nextcan
   can=can+2
   for i=2 to sqrt(can):if (frac(can/i)=0) then goto notprime:fi:next i
   print at(32,17) can;
   label notprime
   if (lower$(inkey$(0))<>"") then
     print at(10,sh) "Wrapping around once ...";
     for x=1 to sw
       a$=getscreen$(0,0,1,sh-2)
       b$=getscreen$(1,0,sw-1,sh-2)
       putscreen b$,0,0
       putscreen a$,sw-1,0
     next x
     sleep 2
     return
   fi
 goto nextcan

 //  Show some animated bitmaps
 label bitmap
   clear screen
   print
   print "Yabasic offers some commands for drawing simple graphics."
   print reverse at(5,12) " Press any key to return to main menu ... "

   n=20
   open window 400,400

   for b=20 to 0 step -1
     color 255-b*12,0,b*12
     fill circle 200,200,b
   next b
   c$=getbit$(179,179,221,221)
   for a=1 to 2000
     color ran(255),ran(255),ran(255)
     x=ran(500)-100:y=ran(500)-100
     fill rectangle ran(500)-100,ran(500)-100,ran(500)-100,ran(500)-100
   next a

   x=200:y=200:phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
   o$=""
   count=0
   label pong
     count=count+1
     if (o$<>"") putbit o$,xo-2,yo-2
     if (count>1000) then
       phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
       sleep 2
       count=0
     endif
     xo=x:yo=y
     x=x+dx:y=y+dy
     o$=getbit$(x-2,y-2,x+46,y+46)
     putbit c$,x,y,"t"
     if (x<0 or x>360) dx=-dx
     if (y<0 or y>360) dy=-dy
     if (inkey$(0)<>"") then
       close window
       return
     endif
   goto pong
 return

 label tetraeder

 open window 400,400
 clear window
 clear screen
 print reverse at(5,12) " Press any key to return to main menu ... "

 dim opoints(4,3)
 restore points
 for n=1 to 4:for p=1 to 3:read opoints(n,p):next p:next n

 dim triangles(4,3)
 restore triangles
 for n=1 to 4:for p=1 to 3:read triangles(n,p):next p:next n

 phi=0:dphi=0.1:psi=0:dpsi=0.05
 dim points(4,3)

 r=60:g=20
 dr=0.5:dg=1.2:db=3
 label main

   phi=phi+dphi
   psi=psi+dpsi
   for n=1 to 4
     points(n,1)=opoints(n,1)*cos(phi)-opoints(n,2)*sin(phi)
     points(n,2)=opoints(n,2)*cos(phi)+opoints(n,1)*sin(phi)
     p2=          points(n,2)*cos(psi)-opoints(n,3)*sin(psi)
     points(n,3)=opoints(n,3)*cos(psi)+ points(n,2)*sin(psi)
     points(n,2)=p2
   next n

   r=r+dr:if (r<0 or r>60) dr=-dr
   g=g+dg:if (g<0 or g>60) dg=-dg
   b=b+db:if (b<0 or b>60) db=-db
   dm=dm+0.01
   m=120-80*sin(dm)
   for n=1 to 4
     p1=triangles(n,1)
     p2=triangles(n,2)
     p3=triangles(n,3)
     n1=points(p1,1)+points(p2,1)+points(p3,1)
     n2=points(p1,2)+points(p2,2)+points(p3,2)
     n3=points(p1,3)+points(p2,3)+points(p3,3)
     if (n3>0) then
       sp=n1*0.5-n2*0.7-n3*0.6
       color 60+r+30*sp,60+g+30*sp,60+b+30*sp
       fill triangle 200+m*points(p1,1),200+m*points(p1,2),200+m*points(p2,1),200+m*points(p2,2),200+m*points(p3,1),200+m*points(p3,2)
     endif
   next n
   if (inkey$(0.1)<>"") close window:return
   clear window
 goto main

 label points
 data  -1,-1,+1,  +1,-1,-1,  +1,+1,+1,  -1,+1,-1
 label triangles
 data  1,2,4,  2,3,4,  1,3,4,  1,2,3

 //  Data section ...
 label mmdata
 //  Data for main menu: Number and text of entries in main menu
 data 4
 data "   Yabasic in a nutshell   "
 data "   Some graphics           "
 data "   A rotating Tetraeder    "
 data "   Exit this demo          "

 Chapter 10. The Copyright of yabasic

 yabasic may be copied under the terms of the MIT License, which is distributed
 with yabasic in the file LICENSE.

 The MIT License grants extensive rights as long as you keep the copyright
 notice present in most files untouched. Here is a list of things that are
 possible under the terms of the MIT License:

   * Put yabasic on your own homepage or CD and even charge for the service of
     distributing yabasic.

   * Write your own yabasic-programs, pack your program and yabasic into a
     package and sell the whole thing.

   * Modify yabasic and add or remove features, sell the modified version
     without adding the sources.

AUTHOR
Marc Ihm, with the input and suggestions from many others.

SEE ALSO
yabasic.htm - for the hyperlinked version of the text that is presented above. www.yabasic.de - for further information on yabasic.

BUGS
Still some.