FOR ••• NEXT¶

Syntax¶

FOR <variable>=x TO y [STEP z]
NEXT [<variable>] [,<variable> ••• ]
where x, y and z are numeric expressions.

Versions: 8K, Extended, Disk

Purpose¶

To allow a series of instructions to be performed in a loop a given number of times.

Remarks¶

The FOR...NEXT loop executes a block of statements a specified number of times, automatically incrementing a counter variable.

Parameters:¶

variable - The loop counter (any numeric variable)
x - Starting value
y - Ending value
z - Step increment (optional, defaults to 1)

Operation:¶

Variable is set to the starting value (x)
Statements in loop body execute
Variable increments by step value (z)
Loop termination test (see below)
If test passes, process repeats from step 2

Loop Termination:¶

The termination test happens AFTER each increment/decrement at the NEXT statement: - Positive STEP (or no STEP): Loop continues while variable <= ending value - Negative STEP: Loop continues while variable >= ending value

For example: - FOR I = 1 TO 10 executes with I=1,2,3,...,10 (10 iterations). After I=10 executes, NEXT increments to 11. Test condition (11 <= 10) is false, loop exits. - FOR I = 10 TO 1 STEP -1 executes with I=10,9,8,...,1 (10 iterations). After I=1 executes, NEXT decrements to 0. Test condition (0 >= 1) is false, loop exits.

Features:¶

STEP can be positive, negative, or fractional (defaults to 1 if omitted)
Loop body may not execute at all if start/end/step values would cause immediate termination (e.g., FOR I=10 TO 1 with positive STEP)
Multiple variables can be specified in NEXT for nested loops (e.g., NEXT J, I)

Example:¶

10 FOR I = 1 TO 10 STEP 2
20   PRINT I;
30 NEXT I

Output: 1 3 5 7 9

Nested Loops:¶

10 FOR I = 1 TO 3
20   FOR J = 1 TO 2
30     PRINT I; J
40   NEXT J, I