Commodore VIC-20 Programmer's Reference Manual page 35

FOR ... TO ... STEP . . .
Format: Abbreviation: Screen Display:
FOR variable = F^.'Lrffi|o Ff
start TO limit [STEP increment]
This is a special BASIC statement that lets you easily use a
variable as a counter. You must specify certain parameters: the
variable name, its starting value, the limit of the count, and how
much to add during each cycle.
Here is a simple BASIC program that counts from 1 to 10,
PRINTing each number and ENDing when complete, and using no
FOR statements:
100 L = 1
110 PRINT L
120 L - L -f- 1
130 IF L <- 10 THEN 110
140 END
Using the FOR statement, here is the same program;
100 FOR L - 1 TO 10
110 PRINT L
120 NEXT L
130 END
As you can seer the program is shorter and easier to understand
using the FOR statement. Here is a closer look at the parameters,
to see how everything works.
The variable can be any numeric variable name except an array
variable. When the program reaches a FOR statement, variable is
set to the value of start. The program proceeds with the statements,
until a statement containing the word NEXT is reached.
At that point, increment is added to variabEe's value. The STEP is
optional, and if there is no STEP shown increment is assumed to be
4-1,
After increment has been added to variable, the vaJue of variable
is compared to limit. It the limit has not been exceeded the program
continues with the line after the FOR statement. If the limit has been
passed, the line to be executed is the line following the NEXT
statement. Note: if the STEP value is positive, variable will exceed
limit when its value is greater than limit, and if the STEP value is
negative, the variable must be less than limit to end the
count. The loop will always be executed at least once, re
gardless of the values in "start" and Lliimit".
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