ITPEC FE Subject B April 2026 Question 8

A is < capacity and B is (front + 1) mod capacity.

This is a circular queue held in a fixed array:

• •Blank A — enqueue may append only while the queue is not full, that is while count < capacity; otherwise it returns false
• •Blank B — after the front element is removed, the front marker steps forward one place and wraps around the end of the array, exactly as rear does in enqueue

The figure confirms it: with front = 3, dequeue clears index 3 and the next front becomes index 4.

Answer (e)

Why not others:
- (a) and (b) — test count < 0, which is never true, so nothing could ever be enqueued
- (g) and (h) — test count > capacity, also never true
- (c) and (d) — test count > 0, which lets an enqueue proceed on a full queue and blocks it on an empty one, both backwards
- (b), (d), (f) and (h) — move the front backwards with front - 1, revisiting the slot just vacated instead of advancing

Key rule: Both markers in a circular buffer advance the same way — add one, then take mod capacity. The fullness test is on count, which is why the array indices alone never tell you whether the queue is full.

AI-generated — may contain errors