Circular Queue · Data Structures and Algorithms

Circular Queue

CSC-211 · Semester III · Data Structures and Algorithms

beginner20 minAvailable

Circular queueFIFO · front & rear wrap around

FR0

Front (next out)

—

Rear (last in)

—

Count

0/ 8

rear = (rear + 1) % 8 · front = (front + 1) % 8 — classic array circular queue.

Lab brief

Objective

See how a circular queue reuses array slots by wrapping the front and rear pointers, avoiding the waste of a linear queue.

Theory & concepts

A linear queue wastes space: once the rear reaches the array end, the queue is 'full' even when the front has left empty slots behind. A circular queue treats the array as a ring — rear wraps to 0 when it passes the end, so every slot is reused. The queue is empty when front equals rear and full when the next rear position equals front (one slot is kept unused to disambiguate).

Rendering diagram…

Circular queue pointer wrap-around

Enqueue → rear := (rear + 1) mod N; arr[rear] := value
Dequeue → front := (front + 1) mod N; value := arr[front]
Empty   → front == rear
Full    → (rear + 1) mod N == front

Prerequisites

Lesson: Arrays and the linked list family
Basic queue behaviour: FIFO

Instructions

1Enqueue values and watch the rear pointer wrap when it reaches the last slot.
2Dequeue values and watch the front pointer advance and wrap.
3Fill the queue and confirm the full condition triggers.
4Dequeue enough to free slots, then enqueue again to see reuse.

Tasks

Wrap the rear
Enqueue N items and watch the rear pointer return to 0.
Reuse slots
Dequeue two, enqueue two, and confirm the freed slots are reused.
Full vs empty
Identify how the sim distinguishes empty from full with one empty slot.

Self-check

Enqueue and dequeue wrap correctly using mod N.
The student explains the one-empty-slot convention.
Slot reuse is observed and described.

Environment

ring layoutfront & rear pointersenqueuedequeuewrap animation