BASIC Flow Control functions
IF THEN
This evaluates a statement to see if it is true and if so executes the code after the then. If the statement is not true then it continues to the next line
Example:
IF 1=1 THEN PRINT "TRUE" TRUE READY.
IF 1=2 THEN PRINT "FALSE" READY.
RUN
This starts executing the BASIC program in memory. If a program calls RUN from inside it will restart the program and program state will be lost (the variables will be reset)
10 PRINT "HELLO" RUN HELLO READY.
10 PRINT "HELLO" 20 RUN RUN HELLO HELLO HELLO ...forever or until you break the program.
END
Ends the running program.
10 GET A$ 20 IF A$ = "Q" THEN END 30 GOTO 10 RUN READY.
STOP
Functions like END but prints the line number the program exited on
10 GET A$ 20 IF A$ = "Q" THEN STOP 30 GOTO 10 RUN BREAK IN 20 READY.
FOR NEXT STEP
FOR variable = start TO end STEP step If STEP is missing then step defaults to 1
When the FOR statement is first called the variable is set to the start value. Then BASIC executes code until the NEXT statement is reached, it then adds the step value (normally 1) to the variable and checks if the variable is going to equal or more (or less if step is negative) than the end value.
10 FOR I = 1 TO 4 20 PRINT I 30 NEXT RUN 1 2 3 4 READY.
10 FOR I = 1 TO 4 STEP 2 20 PRINT I 30 NEXT RUN 1 3 READY.
10 FOR I = 1 TO 4 STEP 3 20 PRINT I 30 NEXT RUN 1 4 READY.
10 FOR I = 1 TO 4 STEP 5 20 PRINT I 30 NEXT RUN 1 READY.
10 FOR I = 4 TO 1 STEP -1 20 PRINT I 30 NEXT RUN 4 3 2 1 READY.
10 FOR I = 4 TO 1 STEP -5 20 PRINT I 30 NEXT RUN 4 READY.
It is also possible to have nested loops. These are FOR loops inside of each other. The internal FOR loop is executed inside the external loop.
10 FOR X = 1 TO 5 20 PRINT X; 30 FOR I = 1 TO 5 40 PRINT I; 50 NEXT I 60 PRINT 70 NEXT X RUN 1 1 2 3 4 5 2 1 2 3 4 5 3 1 2 3 4 5 4 1 2 3 4 5 5 1 2 3 4 5 READY.
It is also possible to combine NEXT statements together
10 FOR X = 1 TO 5 20 FOR I = 1 TO 5 30 PRINT I; 40 NEXT I,X
Is the same as
10 FOR X = 1 TO 5 20 FOR I = 1 TO 5 30 PRINT I; 40 NEXT I 50 NEXT X
Optionally you can leave the variable off the NEXT statement to save memory. This does not work if you combine NEXT statments
10 FOR I = 1 TO 5 20 NEXT
Is the same as
10 FOR I = 1 TO 5 20 NEXT I
GOTO
Start execution at the specified line.
10 PRINT "THIS IS COOL" 20 GOTO 10 RUN THIS IS COOL THIS IS COOL THIS IS COOL ...forever or until you break the program.
GOSUB RETURN
Start execution at specified line and then return to where it was last called.
For example
10 GOSUB 100 20 PRINT "WORLD" 30 END 100 PRINT "HELLO" 110 RETURN RUN HELLO WORLD READY.
Note that GOSUB uses a stack to record where to return to. It has a depth of 23???
10 I = I + 1 20 PRINT I; 30 GOSUB 10 RUN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 ?OUT OF MEMORY ERROR IN 10 READY.
Most programs will never need that much as they only GOSUB 2-3 deep. But it is important to note that if you are doing recursive subroutines you will have to use GOTO and create your own return system.
If you call RETURN without having called GOSUB first you will encounter the following error:
?RETURN WITHOUT GOSUB ERROR IN line#
Where line# is the line number that the return was called from.
CONT
Resumes program execution after RUN/STOP has been pressed or the END or STOP command has been called.
10 FOR I = 1 TO 5 20 PRINT I 30 NEXT I RUN 1 2 3 BREAK IN 20 READY. CONT 4 5
Note you can alter program variables and then resume the program. Also you can examine variable contents and then resume the program.
10 FOR I = 1 TO 2000 20 PRINT I 30 END 40 NEXT I RUN 1 READY. CONT 2 READY.
Note if RUN/STOP and RESTORE is pressed then the program state is lost and CONT won't work.
READY. CONT ?CAN'T CONTINUE ERROR READY.
LIST
LIST will display the contents of the BASIC program stored in memory. It can be given parameters so that the entire program is not listed.
Examples:
10 A=1 20 B=1 30 C=1 40 D=1 LIST 10 A=1 20 B=1 30 C=1 40 D=1 READY. LIST -20 10 A=1 20 B=1 READY. LIST 20- 20 B=1 30 C=1 40 D=1 READY. LIST 20 20 B=1 LIST 20-30 20 B=1 30 C=1 READY. LIST 30-20 READY.
NEW
NEW will delete any BASIC program in memory. It is not often used in a program.
Example:
10 PRINT "HELLO" LIST 10 PRINT "HELLO" READY. NEW READY. LIST READY.
