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Turbo-BASIC XL cheatsheet

Turbo-BASIC XL keywords

+----------+----------+---+----------------------------------------------------------------+
| Keyword  |  Type    |new| Description                                                    |
+----------+----------+---+----------------------------------------------------------------+
| BYE      | control  |no | switch to built-in Self Test program                           |
| CLOAD    | I/O      |no | loads tokenized program from cassette tape (see CSAVE, LOAD)   |
| CLOSE    | I/O      |no | closes a given I/O channel with flush (see OPEN, PUT, GET)     |
| CLR      | memory   |no | clears variables from memory and stack as well                 |
| COLOR    | graphics |no | select/chooses logical color value for drawing                 |
| CONT     | control  |no | continues program execution after STOP statement               |
| CSAVE    | I/O      |no | saves tokenized program into cassette tape (see CLOAD, SAVE)   |
| DATA     | memory   |no | used to store data as list of values (numeric, string)         |
| DEG      | control  |no | switches internal state to enable degrees for trig.functions   |
| DIM      | memory   |no | defines and allocates an array or matrix                       |
| DOS      | control  |no | switch to DOS (Disk Operating System) if available             |
| DRAWTO   | graphics |no | draws a line from current position (PLOT) to given coordinates |
| END      | control  |no | finishes execution of the program and closes open I/O channels |
| ENTER    | I/O      |no | loads and merges into memory a plain text program (in ATASCII) |
| FOR      | control  |no | beginning of a for loop (see TO, STEP, and NEXT)               |
| GET      | I/O      |no | reads one byte from a given I/O channel (see PUT)              |
| GOSUB    | control  |no | jumps to a subroutine, put current line number onto stack      |
| GOTO     | control  |no | jumps to given program line (can be stored in variable)        |
| GO TO    | control  |no | dtto                                                           |
| GRAPHICS | graphics |no | sets the specified graphics node, clear screen for modes < 16  |
| IF       | control  |no | evaluate the condition and executes next commands if true      |
| INPUT    | I/O      |no | read stream from specified I/O channel, converts to num/string |
| LET      | control  |no | assigns a value to a named variable. Fully optional on Atari.  |
| LIST     | I/O      |no | lists the program to screen, printer, or any other device      |
| LOAD     | I/O      |no | loads a tokenized program from specified device (see SAVE)     |
| LOCATE   | graphics |no | read color or character code from specified coordinates        |
| LPRINT   | I/O      |no | prints program source code onto a printer (see PRINT)          |
| NEW      | control  |no | erase program source code, erase all variables too             |
| NEXT     | control  |no | next iteration of a for loop for specified variable (see FOR)  |
| NOTE     | I/O      |no | returns the current position on a given I/O channel (see POINT)|
| ON       | control  |no | used together with GOTO statement to perform computed jump     |
| OPEN     | I/O      |no | initializes and open I/O channel (see CLOSE, PUT, GET)         |
| PLOT     | graphics |no | draws a point (pixel) at given coordinates (see DRAWTO)        |
| POINT    | I/O      |no | sets the current position on a given I/O channel (see NOTE)    |
| POKE     | memory   |no | writes one byte of data into memory location (see DPOKE, PEEK) |
| POP      | control  |no | removes return address from the stack (see GOSUB, RETURN)      |
| POSITION | graphics |no | sets the position of the graphics cursor (see PLOT, DRAWTO)    |
| PRINT    | I/O      |no | writes text to an I/O channel or onto screen if not specified  |
| PUT      | I/O      |no | writer one byte from a given I/O channel (see GET)             |
| RAD      | control  |no | switches internal state to enable radians for trig.functions   |
| READ     | memory   |no | reads data from DATA statement, increment internal DATA ptr.   |
| REM      | comment  |no | used to create a comment in a program (rest of line is ignored)|
| RESTORE  | memory   |no | sets the position where to read data from a DATA statement     |
| RETURN   | control  |no | ends a subroutine, return to statement following GOSUB         |
| RUN      | control  |no | starts execution of a program; can be started from device too  |
| SAVE     | I/O      |no | writes a tokenized program to device (see LOAD)                |
| SETCOLOR | graphics |no | maps a logical color to physical color: hue + level (see COLOR)|
| SOUND    | sound    |no | starts or stops playing a tone on a sound channel (see END)    |
| STATUS   | I/O      |no | returns the status of an I/O channel                           |
| STEP     | control  |no | increment of control variable in a FOR loop (see FOR, TO, NEXT)|
| STOP     | control  |no | stops the program, allowing later resumption (see CONT)        |
| THEN     | control  |no | statement to execute if condition is true in IF (see IF)       |
| TO       | control  |no | limiting condition in a FOR statement (see FOR, NEXT, STEP)    |
| TRAP     | control  |no | when error is encountered, jump to given source line (see GOTO)|
| XIO      | I/O      |no | call the general-purpose I/O routine identified by its number  |
+----------+----------+---+----------------------------------------------------------------+
| BLOAD    | I/O DOS  |yes| loads binary file (with machine instructions)                  |
| BRUN     | I/O DOS  |yes| loads and run binary file (with machine instructions)          |
| DELETE   | DOS      |yes| deletes (erases) file from disk                                |
| DIR      | DOS      |yes| lists files on disk (disk directory)                           |
| RENAME   | DOS      |yes| renames a file                                                 |
| LOCK     | DOS      |yes| lock a file so it can not be changed nor erased                |
| UNLOCK   | DOS      |yes| unlock a file, opposite of LOCK command                        |
| DPOKE    | memory   |yes| writes two bytes of data into two consecutive memory locations |
|          |          |   |                                                                |
+----------+----------+---+----------------------------------------------------------------+

Operators

List of Turbo-BASIC XL operators

+----------+------------+---+---------------------------------+
+ Operator | Type       |new| Description                     |
+----------+------------+---+---------------------------------+
| +        | arithmetic |no | addition                        |
| -        | arithmetic |no | subtraction                     |
| *        | arithmetic |no | multiplication                  |
| /        | arithmetic |no | division                        |
| ^        | arithmetic |no | exponentiation                  |
|          |            |   |                                 |
| AND      | logical    |no | logical conjunction             |
| OR       | logical    |no | logical disjunction             |
| NOT      | logical    |no | logical negation                |
+----------+------------+---+---------------------------------+

Operator +

1 ------------------------------
2 REM Basic usage of + operator
3 REM to add two integer numbers
4 ------------------------------
10 PRINT 1+2
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of + operator
3 REM to add two numbers, one
4 REM integer, second one real
5 ------------------------------
10 PRINT 1+0.5
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of + operator
3 REM to add two variables
4 REM containing integer values
5 ------------------------------
10 A=10
20 B=20
30 PRINT A+B
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of + operator
3 REM to concatenate two strings
4 REM which is not allowed in
5 REM Turbo Basic
6 ------------------------------
10 PRINT "FOO" + "BAR"
998 REM finito
999 STOP

Operator -

1 ------------------------------
2 REM Basic usage of - operator
3 REM to add two numbers
4 ------------------------------
10 PRINT 1-2
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of - operator
3 REM to add two numbers, one
4 REM integer, second real
5 ------------------------------
10 PRINT 1-0.5
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of - operator
3 REM to add two variables
4 ------------------------------
10 A=10
20 B=20
30 PRINT A-B
998 REM finito
999 STOP

1 ------------------------------
2 REM Basic usage of - operator
3 REM to concatenate two strings
4 REM which is not allowed in
5 REM Turbo Basic
6 ------------------------------
10 PRINT "FOO" - "BAR"
998 REM finito
999 STOP

Operator *

1 ------------------------------
2 REM Basic usage of * operator
3 REM to multiply two numbers
4 ------------------------------
10 PRINT 1*2
999 STOP

1 ------------------------------
2 REM Basic usage of * operator
3 REM to multiply two numbers, one
4 REM integer, second real
5 ------------------------------
10 PRINT 3*0.5
999 STOP




## Functions

### List of Turbo-BASIC XL functions

+----------+--------------+---+----------------------------------------------------------------+

  • Function | Type |new| Description | +----------+--------------+---+----------------------------------------------------------------+ | ABS | arithmetic |no | absolute value of a number | | ADR | system |no | address in memory of a string | | ASC | conversion |no | ATASCII value of character | | ATN | goniometric |no | arctangent of a number | | CLOG | logarithmic |no | common logarithm of a number | | CHR$ | string |no | convert an ATASCII value to corresponding character (see VAL) | | COS | goniometric |no | cosine of a number | | EXP | logarithmic |no | exponential function | | FRE | system |no | amount of free memory in bytes | | INT | arithmetic |no | computes floor of a number | | LEN | string |no | returns the length of a string | | LOG | logarithmic |no | natural logarithm of a number | | PADDLE | input device |no | position of a paddle controller | | PEEK | system |no | returns the value at an address in memory (one byte) | | PTRIG | input device |no | indicates whether a paddle trigger is pressed or not | | RND | system |no | a pseudorandom number | | SGN | arithmetic |no | signum of a number | | SIN | goniometric |no | sine of a number | | SQR | arithmetic |no | square root of a number | | STICK | input device |no | a joystick position | | STRIG | input device |no | indicates whether a joystick trigger is pressed or not | | STR$ | string |no | converts a number to string form | | USR | system |no | calls a machine code routine, optionally with parameters | | VAL | string |no | returns the numeric value of a string | | | | | | | DPEEK | memory |yes| reads two bytes of data from two consecutive memory locations | +----------+--------------+---+----------------------------------------------------------------+

### `ABS`

Function `ABS` computes absolute value of a number. Both integers and floating
point numbers are supported by this function.

For negative numbers it returns the number distance from zero:

```basic
1 ------------------------------
2 REM ABS function computation
3 REM for negative integer value
4 ------------------------------
10 PRINT ABS(-10)
999 STOP

For positive numbers, the original value is returned:

1 ------------------------------
2 REM ABS function computation
3 REM for positive integer value
4 ------------------------------
10 PRINT ABS(10)
999 STOP

As mentioned above, it is possible to call this function with floating point number:

1 ------------------------------
2 REM ABS function computation
3 REM for negative float value
4 ------------------------------
10 PRINT ABS(-3.14)
999 STOP

For positive floating point numbers, the original value is returned:

1 ------------------------------
2 REM ABS function computation
3 REM for positive float value
4 ------------------------------
10 PRINT ABS(3.14)
999 STOP

It is forbidden to pass string literal to this function:

1 ------------------------------
2 REM ABS function computation
3 REM for string literal.
4 ------------------------------
10 PRINT ABS("FOO")
999 STOP

Interpreter will detect this issue and insert ERROR flag onto the line:

1 ------------------------------
2 REM ABS function computation
3 REM for string literal.
4 REM Interpreter error detection.
5 ------------------------------
10 ERROR-   PRINT ABS("FOO"<
999 STOP

It is also forbidden to pass string variable to this function:

1 ------------------------------
2 REM ABS function computation
3 REM for string variable.
4 ------------------------------
10 DIM A$(10)
11 A$="FOO"
20 PRINT ABS(A$)
999 STOP

Again interpreter is able to detect such issue and insert ERROR flag onto the appropriate line:

1 ------------------------------
2 REM ABS function computation
3 REM for string variable.
4 REM Interpreter error detection.
5 ------------------------------
10 DIM A$(10)
11 A$="FOO"
20 ERROR-   PRINT ABS(A$<
999 STOP

Plot of ABS function can be displayed by the following example that uses standard graphics mode 8:

1 ------------------------------
2 REM ABS function plot (graph)
3 REM in graphics mode 8
4 ------------------------------
10 EXEC SET_GRAPHICS
20 EXEC DRAW_AXIS
40 REM PLOT FUNCTION
50 FOR X=0 TO 319
60   Y=79-ABS(X-160)
70   IF Y<0 OR Y>159 THEN GOTO 90
80   PLOT X,Y
90 NEXT X
999 STOP 
1000 ------------------------------
1010 REM SET GRAPHICS MODE
1020 ------------------------------
1030 PROC SET_GRAPHICS
1040   GRAPHICS 8
1050   COLOR 1
1060 ENDPROC 
2000 ------------------------------
2010 REM DRAW AXIS
2020 ------------------------------
2030 PROC DRAW_AXIS
2040   PLOT 160,0:DRAWTO 160,159
2050   PLOT 0,80:DRAWTO 319,80
2060   TEXT 0,82,"-160"
2070   TEXT 290,82,"160"
2080   TEXT 162,0,"80"
2090   TEXT 162,150,"-80"
2100   TEXT 162,82,"0,0"
2200 ENDPROC 
2300 ------------------------------

Plot of ABS function with storing the image into BMP format:

The generated image converted into PNG:

images/ABS.png

NOTE

Image with the plotted function having resolution 320x192 pixels with 1 bit per pixel is stored into the standard BMP format onto the file "H:ABS.BMP" (i.e. is is useable in emulators).

1 ------------------------------
2 REM ABS function plot (graph)
3 REM in graphics mode 8
4 ------------------------------
10 EXEC SET_GRAPHICS
20 EXEC DRAW_AXIS
40 REM PLOT FUNCTION
50 FOR X=0 TO 319
60   Y=79-ABS(X-160)
70   IF Y<0 OR Y>159 THEN GOTO 90
80   PLOT X,Y
90 NEXT X
100 DIM FILENAME$(10)
110 FILENAME$="H:ABS.BMP"
120 EXEC WRITE_BMP
999 STOP 
1000 ------------------------------
1010 REM SET GRAPHICS MODE
1020 ------------------------------
1030 PROC SET_GRAPHICS
1040   GRAPHICS 8
1050   COLOR 1
1060 ENDPROC 
2000 ------------------------------
2010 REM DRAW AXIS
2020 ------------------------------
2030 PROC DRAW_AXIS
2040   PLOT 160,0:DRAWTO 160,159
2050   PLOT 0,80:DRAWTO 319,80
2060   TEXT 0,82,"-160"
2070   TEXT 290,82,"160"
2080   TEXT 162,0,"80"
2090   TEXT 162,150,"-80"
2100   TEXT 162,82,"0,0"
2200 ENDPROC 
2300 ------------------------------
10000 ------------------------------
10010 REM Store video RAM
10020 REM in graphics mode 8 into
10030 REM BMP file.
10035 REM 
10040 REM Filename is to be provided
10050 REM via FILENAME$ variable.
10055 REM (Example: "H:TEST.BMP")
10060 ------------------------------
10070 PROC WRITE_BMP
10075   OPEN #1,8,0,FILENAME$
10079   REM write BMP header (32 bytes)
10080   RESTORE 10502
10085   DIM B$(3)
10090   FOR I=0 TO 31
10095     READ B$
10100     B=DEC(B$(2,3))
10110     PUT #1,B
10120   NEXT I
10129   REM write scanlines from last to first
10130   SCANLINE_START=DPEEK(88)
10135   SCANLINE_END=SCANLINE_START+40*191
10140   FOR I=SCANLINE_END TO SCANLINE_START STEP -40
10145     FOR J=0 TO 39
10150       PUT #1,PEEK(I+J)
10155     NEXT J
10160   NEXT I
10165   CLOSE #1
10200 ENDPROC 
10499 ------------------------------
10500 REM BMP file header
10501 REM magic number "BM"
10502 DATA $42,$4D
10503 REM file size=7712 bytes
10504 DATA $20,$1E,$00,$00
10505 REM reserved
10506 DATA $00,$00,$00,$00
10507 REM pixel array offset=32
10508 DATA $20,$00,$00,$00
10509 REM bitmap header size=12 bytes
10510 DATA $0C,$00,$00,$00
10511 REM bitmap width in pixels
10512 DATA $40,$01:REM 320 pixels
10513 REM bitmap height in pixels
10514 DATA $C0,$00:REM 192 pixels
10515 REM number of color planes
10516 DATA $01,$00:REM 1 clr.plane
10517 REM bits per pixel
10518 DATA $01,$00:REM 1 BPP
10519 REM first color in palette
10520 DATA $00,$00,$00
10521 REM second color in palette
10522 DATA $FF,$FF,$FF
10523 REM end of BMP file header

ADR

Function ADR returns address of a string stored in memory. Can be used to store subroutines written in machine code and encoded into string.

In the following example, the memory is allocated for a string, string is initialized and then its address is printed:

1 ------------------------------
2 REM ADR function computation
3 REM for pre-allocated string
4 ------------------------------
10 DIM A$(10)
20 A$="FOO"
30 PRINT ADR(A$)
998 REM finito
999 STOP

Strings allocated in sequence are usually stored in consecutive memory blocks as can be tested by this example:

1 ------------------------------
2 REM ADR function computation
3 REM for pre-allocated strings
4 ------------------------------
10 DIM A$(10),B$(10),C$(10)
20 PRINT ADR(A$)
30 PRINT ADR(B$)
40 PRINT ADR(C$)
998 REM finito
999 STOP

It is possible to get an address for in-place string literal (which make sense for storing machine code, for example):

1 ------------------------------
2 REM ADR function computation
3 REM for string literals
4 ------------------------------
10 PRINT ADR("FOO")
20 PRINT ADR("BAR")
30 PRINT ADR("BAZ")
998 REM finito
999 STOP

ASC

Function ASC returns ATASCII value of input character. Because Turbo-BASIC XL does not distinguish between characters and strings, it is needed to pass string parameter to this function. It means it is possible to pass a multi character string or an empty string as well into ASC. These three possibilities are shown in following examples.

Normal usage of ASC function is based on passing a string containing with just one character. In this case, ATASCII value of such character is returned:

1 ------------------------------
2 REM ASC function computation
3 REM for string literal with
4 REM one character
5 ------------------------------
10 PRINT ASC("A")
998 REM finito
999 STOP

It is also possible to call this function with longer string. In this case, the ATASCII value of the first character from the string is returned:

1 ------------------------------
2 REM ASC function computation
3 REM for string literal with
4 REM multiple characters
5 ------------------------------
10 PRINT ASC("ABC")
998 REM finito
999 STOP

When empty string is passed, value 44 is returned (ATASCII value for comma):

1 ------------------------------
2 REM ASC function computation
3 REM for empty string literal
4 ------------------------------
10 PRINT ASC("")
998 REM finito
999 STOP

TODO: check why this happens.

ATN

Function ATN computes arctangent of a given input number. It is possible to select DEG mode for getting results in degress, or RAD mode for getting results in radians.

ATN function computation for selected input values in DEG mode:

1 ------------------------------
2 REM ATN function computation
3 REM for selected input values
4 REM in DEG mode
5 ------------------------------
10 DEG 
20 RESTORE 100
30 FOR I=1 TO 7
40   READ X
50   PRINT X,ATN(X)
60 NEXT I
100 DATA -1E20, -1, -0.5
110 DATA 0
120 DATA 0.5, 1, 1E20
998 REM finito
999 STOP

ATN function computation for selected input values in RAD mode:

1 ------------------------------
2 REM ATN function computation
3 REM for selected input values
4 REM in RAD mode
5 ------------------------------
10 RAD 
20 RESTORE 100
30 FOR I=1 TO 7
40   READ X
50   PRINT X,ATN(X)
60 NEXT I
100 DATA -1E20, -1, -0.5
110 DATA 0
120 DATA 0.5, 1, 1E20
998 REM finito
999 STOP

Display of ATN function (simplest variant):

1 ------------------------------
2 REM ATN function plot
4 REM in DEG mode
5 ------------------------------
10 DEG 
20 GRAPHICS 8
30 COLOR 1
40 PLOT 160,0:DRAWTO 160,159
50 PLOT 0,80:DRAWTO 319,80
60 FOR X=0 TO 319
70   Y=79-0.8*ATN((X-160)/2)
80   PLOT X,Y
90 NEXT X
998 REM finito
999 STOP

Plot of ATN function can be displayed by the following example that uses standard graphics mode 8, display axis etc.:

1 ------------------------------
2 REM ATN function plot
4 REM in DEG mode
5 ------------------------------
10 DEG 
20 EXEC SET_GRAPHICS
30 EXEC DRAW_AXIS
40 REM PLOT FUNCTION
50 FOR X=0 TO 319
60   Y=79-0.8*ATN((X-160)/2)
70   IF Y<0 OR Y>159 THEN GOTO 90
80   PLOT X,Y
90 NEXT X
998 REM finito
999 STOP 
1000 ------------------------------
1010 REM SET GRAPHICS MODE
1020 ------------------------------
1030 PROC SET_GRAPHICS
1040   GRAPHICS 8
1050   COLOR 1
1060 ENDPROC 
2000 ------------------------------
2010 REM DRAW AXIS
2020 ------------------------------
2030 PROC DRAW_AXIS
2040   PLOT 160,0:DRAWTO 160,159
2050   PLOT 0,80:DRAWTO 319,80
2060   TEXT 0,82,"-80"
2070   TEXT 290,82,"80"
2080   TEXT 162,5,"90"
2090   TEXT 162,145,"-90"
2100   TEXT 162,82,"0,0"
2200 ENDPROC 
2300 ------------------------------

Plot of ATN function with storing the image into BMP format:

The generated image converted into PNG:

images/ATN.png

NOTE

Image with the plotted function having resolution 320x192 pixels with 1 bit per pixel is stored into the standard BMP format onto the file "H:ABS.BMP" (i.e. is is useable in emulators).



CHR$


1 ------------------------------
2 REM CHR$ function computation
3 REM for selected integer input
4 REM value
5 ------------------------------
10 PRINT CHR$(42)
998 REM finito
999 STOP



1 ------------------------------
2 REM CHR$ function computation
3 REM for selected integer input
4 REM value which is larger than
5 REM 255
6 ------------------------------
10 PRINT CHR$(1234)
998 REM finito
999 STOP



1 ------------------------------
2 REM CHR$ function computation
3 REM for selected floating
4 REM input value
5 ------------------------------
10 PRINT CHR$(42.3)
998 REM finito
999 STOP



COS


1 ------------------------------
2 REM COS function computation
3 REM for selected input values
4 REM in DEG mode
5 ------------------------------
10 DEG 
20 PRINT COS(0)
30 PRINT COS(30)
40 PRINT COS(45)
50 PRINT COS(60)
60 PRINT COS(90)
998 REM finito
999 STOP



1 ------------------------------
2 REM COS function computation
3 REM for selected input values
4 REM in RAD mode
5 ------------------------------
10 RAD 
20 PRINT COS(0)
30 PRINT COS(30)
40 PRINT COS(45)
50 PRINT COS(60)
60 PRINT COS(90)
998 REM finito
999 STOP



1 ------------------------------
2 REM COS function plot for DEG
3 REM mode (positive X values)
4 ------------------------------
10 DEG 
20 GRAPHICS 8
30 COLOR 1
40 PLOT 0,0:DRAWTO 0,159
50 PLOT 0,80:DRAWTO 319,80
60 FOR X=0 TO 319
70   Y=79-60*COS(X*360/320)
80   PLOT X,Y
90 NEXT X
998 REM finito
999 STOP 



FRE


1 ------------------------------
2 REM FRE function with formal
3 REM parameter set to zero
4 REM value (as usual)
5 ------------------------------
10 PRINT FRE(0)
998 REM finito
999 STOP



1 ------------------------------
2 REM FRE function with formal
3 REM parameter set to non zero
4 REM value (which is legit)
5 ------------------------------
10 PRINT FRE(42)
998 REM finito
999 STOP



1 ------------------------------
2 REM FRE function with formal
3 REM parameter set to float
4 REM value (which is legit)
5 ------------------------------
10 PRINT FRE(3.1415)
998 REM finito
999 STOP



SIN


1 ------------------------------
2 REM SIN function computation
3 REM for selected input values
4 REM in DEG mode
5 ------------------------------
10 DEG 
20 PRINT SIN(0)
30 PRINT SIN(30)
40 PRINT SIN(45)
50 PRINT SIN(60)
60 PRINT SIN(90)
998 REM finito
999 STOP



1 ------------------------------
2 REM SIN function computation
3 REM for selected input values
4 REM in RAD mode
5 ------------------------------
10 RAD 
20 PRINT SIN(0)
30 PRINT SIN(30)
40 PRINT SIN(45)
50 PRINT SIN(60)
60 PRINT SIN(90)
998 REM finito
999 STOP



1 ------------------------------
2 REM SIN function plot for DEG
3 REM mode (positive X values)
4 ------------------------------
10 DEG 
20 GRAPHICS 8
30 COLOR 1
40 PLOT 0,0:DRAWTO 0,159
50 PLOT 0,80:DRAWTO 319,80
60 FOR X=0 TO 319
70   Y=79-60*SIN(X*360/320)
80   PLOT X,Y
90 NEXT X
998 REM finito
999 STOP 



1 ------------------------------
2 REM SIN and COS functions can
3 REM be used to plot circle
4 REM (which is very slow)
5 ------------------------------
10 DEG 
20 GRAPHICS 8
30 COLOR 1
40 PLOT 0,0:DRAWTO 0,159
50 PLOT 0,80:DRAWTO 319,80
60 FOR X=0 TO 319
70   Y=79-60*SIN(X*360/320)
75   PLOT X,Y
80   Y=79-60*COS(X*360/320)
85   PLOT X,Y
90 NEXT X
998 REM finito
999 STOP



Loops


Four types of loops are supported by Turbo-BASIC XL:


    

  • FOR-NEXT (taken from Atari BASIC with one bug fix)
    • 

  • DO-LOOP
    • 

  • REPEAT-UNTIL
    • 

  • WHILE-WEND
    • 



FOR-NEXT


This variant of loop construct was taken from Atari BASIC, including the bug mentioned below. Because Turbo-BASIC XL is designed to be as compatible with Atari BASIC as possible, the buggy behaviour can be switched on or turn off.


    

  • Basic usage of this loop:
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM legal start and stop
4 REM values and default STEP
5 REM parameter that is equal
6 REM to 1.
7 ------------------------------
10 FOR I=0 TO 10
20   PRINT I
30 NEXT I
998 REM finito
999 STOP



    

  • Default step value is set to 1, but it can be specified explicitly if needed:
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM legal start and stop
4 REM values and explicit STEP
5 REM parameter.
6 ------------------------------
10 FOR I=0 TO 10 STEP 2
20   PRINT I
30 NEXT I
998 REM finito
999 STOP



    

  • Counting downward
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM legal start and stop
4 REM values and negative STEP
5 REM parameter that must be
6 REM set explicitly.
7 ------------------------------
10 FOR I=10 TO 0 STEP -2
20   PRINT I
30 NEXT I
998 REM finito
999 STOP



    

  • Improper usage (revealing bug in Atari BASIC)
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM illlegal start and stop
4 REM values and default STEP
5 REM parameter that is equal
6 REM to 1.
7 ------------------------------
10 FOR I=10 TO 0
20   PRINT I
30 NEXT I
998 REM finito
999 STOP



    

  • Controlling FOR-NEXT loop behaviour by *F - option
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM illegal start and stop
4 REM values.
5 REM
6 REM Usage of "*F -" option
7 REM that affects FOR-LOOP
8 REM behaviour.
9 ------------------------------
10 *F -
20 FOR I=10 TO 0
30   PRINT I
40 NEXT I
998 REM finito
999 STOP



    

  • Controlling FOR-NEXT loop behaviour by *F + option
    • 



1 ------------------------------
2 REM FOR-NEXT statement with
3 REM illegal start and stop
4 REM values.
5 REM
6 REM Usage of "*F +" option
7 REM that affects FOR-LOOP
8 REM behaviour.
9 ------------------------------
10 *F +
20 FOR I=10 TO 0
30   PRINT I
40 NEXT I
998 REM finito
999 STOP



    

  • Pi computation based on usage of nested FOR-NEXT loops:
    • 



1 ------------------------------
2 REM PI computation based on
3 REM usage of FOR-NEXT loops
4 ------------------------------
10 N=1
20 FOR I=1 TO 10
25   EXEC COMPUTE_PI
30   PRINT I,N,PI
35   N=N*2
40 NEXT I
998 REM finito
999 STOP
1000 ------------------------------
1001 REM SUBRUTINA PRO VYPOCET PI
1002 PROC COMPUTE_PI
1010   PI=4
1020   FOR J=3 TO N+2 STEP 2
1030     PI=PI*(J-1)/J*(J+1)/J
1040   NEXT J
1050 ENDPROC 



DO-LOOP


REPEAT-UNTIL


1 ------------------------------
2 REM REPEAT-UNTIL loop with
3 REM one control variable
4 REM that is increased by one
5 REM in each iteration
6 ------------------------------
10 A=0
20 REPEAT 
30   A=A+1
40   PRINT A
50 UNTIL A=10
998 REM finito
999 STOP



1 ------------------------------
2 REM REPEAT-UNTIL loop with
3 REM one control variable
4 REM which value is doubled
5 REM in each iteration
6 ------------------------------
10 A=1
20 REPEAT 
30   PRINT A
40   A=A*2
50 UNTIL A>1024
998 REM finito
999 STOP



1 ------------------------------
2 REM Nested REPEAT-UNTIL loops
3 ------------------------------
10 A=1
20 REPEAT 
30   B=10
40   REPEAT 
50     PRINT A*B;" ";
60     B=B+1
70   UNTIL B>20
80   A=A+1
90   PRINT 
95 UNTIL A>6
998 REM finito
999 STOP



1 ------------------------------
2 REM PI computation based on
3 REM REPEAT-UNTIL loops
4 ------------------------------
10 N=1
20 REPEAT 
25   EXEC COMPUTE_PI
30   PRINT N,PI
35   N=N*2
40 UNTIL N>2000
998 REM finito
999 STOP
1000 ------------------------------
1001 REM SUBRUTINA PRO VYPOCET PI
1002 PROC COMPUTE_PI
1010   PI=4
1015   J=3
1020   REPEAT 
1030     PI=PI*(J-1)/J*(J+1)/J
1040     J=J+2
1050   UNTIL J>N+2
1060 ENDPROC 



WHILE-WEND