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Loops Star


"Loops" make it easier to do an action multiple times. There are at least four types of loops: IF...GOTO, WHILE...WEND, DO...LOOP, and FOR...NEXT.


IF...GOTO

This program uses IF...GOTO to create a loop:

    x = 10

    start:
    PRINT x

    x = x + 1      (This adds 1 to x)

    IF x < 15 THEN GOTO start
Output:
    10
    11
    12
    13
    14

WHILE...WEND

The WHILE...WEND commands continue a loop until a specified expression is false.

To use WHILE...WEND:
  1. Place an expression after WHILE

  2. Enter a list of commands

  3. Place WEND at the end


Run the following:
    x = 10

    WHILE x < 15

      PRINT x

      x = x + 1

    WEND
Output (same as in previous example):
    10
    11
    12
    13
    14

DO...LOOP

DO...LOOP is exactly the same as WHILE...WEND, except it has at least two slight advantages. With DO...LOOP you can:
  1. Loop until an expression is true

  2. Loop at least one time regardless of whether the expression is true or not.


To use DO...LOOP:
  1. Specify whether the loop continues "while" the expression is true or "until" the expression is true, using the WHILE and UNTIL statements, respectively.

  2. Place an expression after WHILE/UNTIL

  3. Enter a list of commands

  4. Place LOOP at the end


The following uses the WHILE statement:
    x = 10

    DO WHILE x < 15

      PRINT x

      x = x + 1

    LOOP

This program uses the UNTIL statement:
    x = 10

    DO UNTIL x = 15

      PRINT x

      x = x + 1

    LOOP

They both output:
    10
    11
    12
    13
    14

If you place the expression at the end of the loop instead, the program goes through the loop at least once.
    x = 32

    DO

      PRINT x

      x = x + 1

    LOOP WHILE x < 5
This is the output because the loop was only gone through one time:
    32

FOR...NEXT

FOR...NEXT provides an easier way to create a loop.

    FOR x = 1 TO 5

      PRINT x

    NEXT x
Output:
    1
    2
    3
    4
    5

TIP: The X after NEXT is optional (unless you have a loop within a loop).


Also, you can use the STEP attribute to specify how much X will be increased each time through the loop.
    FOR x = 1 TO 5 STEP 2

      PRINT x

    NEXT x
Output:
    1
    3
    5

STOPPING LOOPS

To stop a loop prematurely, use the EXIT command, followed by either FOR or DO.
    FOR x = 1 TO 5

      PRINT x

      IF (x = 3) THEN EXIT FOR

    NEXT x
Output:
    1
    2
    3
(NOTE: This command only works with the DO...LOOP and FOR...NEXT commands, not with WHILE...WEND or IF...GOTO.)


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