Do Loops with a Loop Condition

The following program adds something to the DO statement:

' Loop with a loop condition
'
LET COUNT = 0            'Statement 1

DO WHILE COUNT <= 2      'Statement 2
  PRINT COUNT            'Statement 3
  LET COUNT = COUNT + 1  'Statement 4 
LOOP 

END

COUNT <= 2 is called a loop condition. It says under what condition the loop body (statements 3 and 4) will execute.

The loop body is executed only if COUNT is less than or equal to 2. If the loop body can't start, the next statement after LOOP is executed.

Here is how the program works:

• COUNT is set to 0.
• At the DO statement: COUNT is less than or equal to 2 so the loop body is executed.
  • PRINT COUNT prints 0.
  • One is added to COUNT, so now COUNT is 1.
  • The LOOP sends execution back to the DO.
• At the DO statement: COUNT is less than or equal to 2 so the loop body is executed.
  • PRINT COUNT prints 1.
  • One is added to COUNT, so now COUNT is 2.
  • The LOOP send execution back to the DO.
• At the DO statement: COUNT is less than or equal to 2 so the loop body is executed.
  • PRINT COUNT prints 2.
  • One is added to COUNT, so now COUNT is 3.
  • The LOOP sends execution back to the DO.
• At the DO statement: COUNT is NOT less than or equal to 2 so the loop body is skipped over.
• The END is executed, ending the program.

The loop ended gracefully. Just before the loop body COUNT is tested. If it is less than or equal to two, the loop body is executed. Otherwise the statement after LOOP is executed.