REPEAT…UNTIL loop, also known as a post-controlled loop, which is an important topic in the Computer Science 2210 syllabus. The lesson begins by explaining that a REPEAT…UNTIL loop is different from other loops because the condition is checked after the statements inside the loop have been executed. This means the loop will always run at least once, making it especially useful in situations where input must be taken from the user before any condition can be tested, such as menu selection or input validation.
The lesson then explains the basic structure of the REPEAT…UNTIL loop and how it works in practice. Students are shown how the program first executes the statements inside the loop, such as displaying a message and taking input, and only then checks the condition at the end. If the condition is false, the loop repeats; if the condition becomes true, the loop stops. A clear pseudocode example is discussed where a user is asked to enter a number between 1 and 10. The program continues to ask for input using the REPEAT…UNTIL loop until the number falls within the valid range, helping students understand how validation is handled using this loop.
Another example used in the lesson is a menu-driven program, where the menu options are displayed at least once and the user must enter a valid choice. This reinforces the idea that REPEAT…UNTIL is ideal when the program must execute at least one time regardless of the input. By the end of the lesson, students understand the advantages of using a post-controlled loop, including improved program clarity, reduced repetition, and effective input validation. The lesson helps students confidently write and explain REPEAT…UNTIL loops using exam-standard pseudocode, preparing them well for Cambridge O-Level 2210 examination questions.