WHILE NotSolved … Instructions here ... FOR i ← 1 TO 5 … Instructions here…

The idea

This pseudocode shows nested iteration: a FOR loop counting i from 1 to 5 sits inside a WHILE loop that continues while NotSolved is true. Trace it by working outwards. The WHILE condition is tested first; if NotSolved is true, the body runs. Inside, the FOR loop executes its instructions five times (i = 1, 2, 3, 4, 5), then the instructions after ENDFOR run once, then the WHILE condition is retested. So each WHILE pass performs five FOR passes plus the trailing instructions. The FOR loop restarts from i = 1 on every WHILE pass. The WHILE ends when NotSolved becomes false, which must happen inside the body or the loop never terminates.

What earns the marks

• Identifies the WHILE loop as the outer loop and the FOR loop as the inner loop.
• States that the FOR loop executes five times (i = 1 to 5) for each pass of the WHILE loop.
• Explains that the instructions after ENDFOR run once per WHILE pass, after the FOR loop completes.
• Recognises that the WHILE condition is retested after the body finishes and that NotSolved must change to end the loop.
• Notes that the FOR loop restarts from i = 1 on each new WHILE pass.

Common mistakes and how to put them right

• Thinking the FOR loop runs only once in total.

  Put it right: It restarts and runs five times on every WHILE pass.

• Believing the trailing instructions run inside the FOR loop.

  Put it right: They sit after ENDFOR, so they run once per WHILE pass.

• Ignoring termination; correction: NotSolved must be set to false somewhere in the body or the WHILE never ends.

Exam tips

• Label the outer and inner loops before tracing any values.
• Track i through 1 to 5 for one WHILE pass, then note the loop resets.
• Check where NotSolved is updated to confirm the loop can terminate.