Programming concepts: REPEAT … Instructions here … UNTIL Solved

The idea

REPEAT … UNTIL is AQA pseudocode for indefinite (condition controlled) iteration with the condition at the end. The instructions between REPEAT and UNTIL form the loop body and run at least once. After the body, the condition following UNTIL is tested; if it is false the body repeats, and if it is true the loop ends. In the example, the loop keeps running until the variable Solved becomes true. Because the test is at the end, the body is guaranteed to execute at least once, unlike a WHILE loop. A common use is repeatedly reading input or processing steps until a success flag is set. Reading the structure from top to bottom shows the order: body first, then condition.

What earns the marks

• Recognises REPEAT … UNTIL as indefinite (condition controlled) iteration.
• States that the instructions in the body execute before the condition is tested.
• Explains that the loop repeats while the condition is false and terminates when it is true.
• Notes that the body runs at least once because the condition is at the end.
• Interprets UNTIL Solved as continuing until the variable Solved becomes true.

Common mistakes and how to put them right

• Believing the condition is checked before the body runs.

  Put it right: The body runs first, then UNTIL is tested.

• Thinking the loop ends when Solved is false.

  Put it right: It repeats until Solved is true.

• Treating REPEAT … UNTIL as a fixed-count loop.

  Put it right: It is indefinite, controlled by a condition.

Exam tips

• Trace the loop step by step: run the body, then evaluate the UNTIL condition.
• State clearly that the body executes at least once.
• Explain the difference between repeating while false and stopping when true.