For Next

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FOR counter = initial_value to final_value [STEP step_value]
   [loop body]
NEXT counter

A FOR LOOP allows you to specify that an application should repeat a statement or set of statements until a counter reaches its final_value.

The loop body may consist of zero or more statements. However, the use of at least one statement in the loop body is encouraged for clarity.

The optional numeric step_value following the STEP keyword specifies by how much to increase or decrease the counter variable with each execution of the FOR LOOP. If the STEP keyword is absent and step_value isn't specified, then the default value of +1 is used. If step_value is negative, then the counter variable is decreased with each execution of the loop.

Although it is not required to indent the body of a FOR LOOP, it is highly recommended to indent it for readability.

Syntax

ForNext.png

Examples

This example prints integers from 1 to 100:

00010 for counter = 1 to 100
00020    print counter
00030 next counter

The same effect may be achieved by this program:

00010 for counter = 1 to 100 step 1 ! this is redundant, since the default value of 1 is used anyway.
00020    print counter
00030 next counter

This program prints numbers from 100 to 1 in descending order:

00010 for counter = 100 to 1 step -1
00020    print counter
00030 next counter

This program prints EVEN numbers from 2 to 100 in ascending order:

00010 for counter = 2 to 100 step 2
00020    print counter
00030 next counter 

Best Practices

Although the value of the LOOP COUNTER VARIABLE can be changed in the body of a for loop, avoid doing so, because this practice can lead to subtle errors.

For example, it is impossible to tell how many times the following loop will execute, because the user may change the value of the loop counter each time the loop executes

00010 for i = 1 to 10
00020    print "Enter a value"
00030    input i
00040 next i

Loop Performance

In loops, avoid calculations for which the result never changes—such calculations should typically be placed before the loop.