Circular Queue Implementation Using Array in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a circular queue?

A circular queue is a type of queue where the last position is connected back to the first position to make a circle. It allows efficient use of space by reusing empty slots after dequeue operations.

beginner

How do you check if a circular queue is full?

The circular queue is full when the next position of rear is equal to front. In formula: (rear + 1) % size == front.

intermediate

What happens to front and rear pointers when you enqueue an element in a circular queue?

When enqueueing, rear moves forward by one position using (rear + 1) % size. If the queue was empty, front is set to 0.

intermediate

How do you dequeue an element from a circular queue?

Remove the element at front, then move front forward by one using (front + 1) % size. If after dequeue front becomes equal to rear + 1 (mod size), reset both to -1 (empty queue).

beginner

Why is a circular queue better than a simple linear queue using arrays?

A circular queue reuses empty spaces freed by dequeued elements, avoiding wasted space and the need to shift elements. A linear queue wastes space once rear reaches the end.

What condition indicates that a circular queue is empty?

A front == -1 and rear == -1

B front == rear

C (rear + 1) % size == front

D rear == size - 1

The queue is empty when both front and rear are -1.

If the queue size is 5, front is 3, and rear is 1, is the queue full?

A No, because rear < front

B Yes, because (rear + 1) % size == front

C No, because front != rear

D Yes, because rear == size - 1

Calculate (1 + 1) % 5 = 2, which is not equal to front (3), so queue is not full. Correct answer is No, so option A is wrong. Correct answer is C.

What is the formula to move rear pointer forward in a circular queue?

A rear = rear + 1

B rear = rear - 1

C rear = front + 1

D rear = (rear + 1) % size

Rear moves forward circularly using modulo operation.

After dequeuing the last element, what should front and rear be set to?

A front = rear = 0

B front = 0, rear = size - 1

C front = rear = -1

D front = rear = size

Setting both to -1 indicates the queue is empty.

Why do we use modulo (%) operator in circular queue?

A To reset pointers to zero when they reach the end

B To check if queue is empty

C To increase queue size

D To sort the queue elements

Modulo helps wrap pointers back to start to form a circle.

Explain how enqueue and dequeue operations work in a circular queue using an array.

Think about how the pointers move in a circle.

Describe the advantages of using a circular queue over a simple linear queue implemented with arrays.

Consider what happens when the rear reaches the end of the array.