Loops

Loops repeat a block of instructions. They are useful for processing a sequence, validating input, or running a calculation several times.

WHILE loops#

A WHILE loop repeats while its condition remains true.

1counter = 02​3WHILE counter < 34  PRINT counter5  counter = counter + 16END

The output is:

102132

The loop has three parts:

1. initialize the state before the loop;
2. check a condition before every iteration;
3. update the state inside the loop.

FOR loops#

Use FOR when the start, end, and step are known in advance.

1FOR number = 1 TO 52  PRINT number3END

Add STEP to change the increment:

1FOR number = 10 TO 0 STEP -22  PRINT number3END

Choose the right loop#

Avoid infinite loops#

An infinite loop never makes its condition false.

1counter = 02WHILE counter < 53  PRINT counter4END

The update is missing

The example never changes counter. Add counter = counter + 1 inside the loop before running it.

Nested loops#

A loop may contain another loop. Use indentation to keep the structure readable.

1FOR row = 1 TO 32  FOR column = 1 TO 33    PRINT row * column4  END5END

Nested loops can perform many operations, so check the expected number of iterations before using them with large ranges.