Programming concepts: An example of nested iteration would be:

The idea

Nested iteration means one loop placed inside the body of another loop, so the inner loop runs completely for each single pass of the outer loop. To judge an example, trace the structure: identify the outer loop, find the inner loop inside its body, and check that the inner loop restarts each time the outer loop repeats. For instance, an outer FOR counting rows 1 to 3 containing an inner FOR counting columns 1 to 4 produces 3 × 4 = 12 inner passes. A single loop, or two loops written one after another rather than one inside the other, is sequential iteration, not nested. When answering, look for the containment of one loop within another's body and be ready to state how many times the inner instructions execute.

What earns the marks

• Identifies that nested iteration requires one loop contained within the body of another loop.
• Distinguishes nesting (one loop inside another) from sequential loops written one after the other.
• Recognises that the inner loop completes all its repetitions for each single pass of the outer loop.
• Can state the total number of inner executions as the product of the outer and inner repetition counts, e.g. 3 × 4 = 12.

Common mistakes and how to put them right

• Treating two loops written consecutively as nested.

  Put it right: Nesting requires the inner loop to sit inside the outer loop's body.

• Assuming the inner loop runs only once overall.

  Put it right: It restarts and completes for every pass of the outer loop.

• Adding the loop counts instead of multiplying.

  Put it right: Total inner passes equal outer count × inner count.

Exam tips

• Underline the outer loop and the inner loop in the code before choosing an option.
• Check containment: the inner loop must appear between the outer loop's start and end.
• If counts are given, multiply outer repetitions by inner repetitions to confirm the total.