Commodore 128D - Page 274

FOR/TO/STEP/
NEXT
—Define a repetitive program loop structure.
FOR variable = start value TO end value [STEP increment]
NEXT variable
This statement works with the NEXT statement to set up a section of
the program (i.e., a loop) that repeats for a set number of times. This
is useful when something needs to be counted or something must be
done a certain number of times (such as printing).
This statement executes all the commands enclosed between the
FOR and NEXT statements repetitively, according to the start and
end values. The start value and the end value are the beginning and
ending counts for the loop variable. The loop variable is added to or
subtracted from during the FOR/NEXT loop.
The logic of the FOR/NEXT statement is as follows. First, the loop
variable is set to the start value. When the program reaches a pro
gram line containing the NEXT statement, it adds the STEP incre
ment (default = 1) to the value of the loop variable and checks to
see if it is higher than the end value of the loop. If the loop variable is
less than or equal to the end value, the loop is executed again, start
ing with the statement immediately following the FOR statement. If
the loop variable is greater than the end value, the loop terminates
and the program resumes immediately following the NEXT state
ment. The opposite is true jf the step size is negative.
EXAMPLE:
10 FOR L = 1 TO 10
20 PRINT L
30 NEXT L
40 PRINT "I'M DONE! L = "L
This program prints the numbers from one to 10 followed by the mes
sage I'M DONE! L = 11.
The end value of the loop may be followed by the word STEP and
another number or variable. In this case, the value following the
STEP is added each time instead of one. This allows counting back
wards, by fractions, or in increments other than one.
The user can set up loops inside one another. These are known as
nested loops. Care must be taken when nesting loops so the last
loop to start is the first one to end.
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BASIC 7.0 ENCYCLOPEDIA—Basic Commands and Statements