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Circular Queue Operations

A circular queue is a queue where the last element is connected to the first element, forming a circular structure. This solves the issue of empty space occurring in regular queues after elements are inserted and deleted. A circular queue uses two pointers, front and rear, to track the first and last elements, and implements enqueue and dequeue by circularly incrementing these pointers. The queue is considered full if front is equal to rear + 1 or if front is 0 and rear is the maximum size - 1.

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112 views4 pages

Circular Queue Operations

A circular queue is a queue where the last element is connected to the first element, forming a circular structure. This solves the issue of empty space occurring in regular queues after elements are inserted and deleted. A circular queue uses two pointers, front and rear, to track the first and last elements, and implements enqueue and dequeue by circularly incrementing these pointers. The queue is considered full if front is equal to rear + 1 or if front is 0 and rear is the maximum size - 1.

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akurathikotaiah
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A circular queue is the extended version of a regular queue where the last element is

connected to the first element. Thus forming a circle-like structure.

The circular queue solves the major limitation of the normal queue. In a normal queue,

after a bit of insertion and deletion, there will be non-usable empty space.

Here, indexes 0 and 1 can only be used after resetting the queue (deletion of all
elements). This reduces the actual size of the queue.

Circular Queue Operations


The circular queue work as follows:
 two pointers FRONT and REAR
 FRONT track the first element of the queue
 REAR track the last elements of the queue
 initially, set value of FRONT and REAR to -1

1. Enqueue Operation
 check if the queue is full
 for the first element, set value of FRONT to 0
 circularly increase the REAR index by 1 (i.e. if the rear reaches the end, next it would be
at the start of the queue)
 add the new element in the position pointed to by REAR

2. Dequeue Operation
 check if the queue is empty
 return the value pointed by FRONT
 circularly increase the FRONT index by 1
 for the last element, reset the values of FRONT and REAR to -1

However, the check for full queue has a new additional case:
 Case 1: FRONT = 0 && REAR == SIZE - 1
 Case 2: FRONT = REAR + 1
The second case happens when REAR starts from 0 due to circular increment and when
its value is just 1 less than FRONT, the queue is full.

// Circular Queue implementation in C

#include <stdio.h>

#define SIZE 5

int items[SIZE];
int front = -1, rear = -1;

// Check if the queue is full


int isFull() {
if ((front == rear + 1) || (front == 0 && rear == SIZE - 1)) return 1;
return 0;
}
// Check if the queue is empty
int isEmpty() {
if (front == -1) return 1;
return 0;
}

// Adding an element
void enQueue(int element) {
if (isFull())
printf("\n Queue is full!! \n");
else {
if (front == -1) front = 0;
rear = (rear + 1) % SIZE;
items[rear] = element;
printf("\n Inserted -> %d", element);
}
}

// Removing an element
int deQueue() {
int element;
if (isEmpty()) {
printf("\n Queue is empty !! \n");
return (-1);
} else {
element = items[front];
if (front == rear) {
front = -1;
rear = -1;
}
// Q has only one element, so we reset the
// queue after dequeing it. ?
else {
front = (front + 1) % SIZE;
}
printf("\n Deleted element -> %d \n", element);
return (element);
}
}

// Display the queue


void display() {
int i;
if (isEmpty())
printf(" \n Empty Queue\n");
else {
printf("\n Front -> %d ", front);
printf("\n Items -> ");
for (i = front; i != rear; i = (i + 1) % SIZE) {
printf("%d ", items[i]);
}
printf("%d ", items[i]);
printf("\n Rear -> %d \n", rear);
}
}
int main() {
// Fails because front = -1
deQueue();

enQueue(1);
enQueue(2);
enQueue(3);
enQueue(4);
enQueue(5);

// Fails to enqueue because front == 0 && rear == SIZE - 1


enQueue(6);

display();
deQueue();

display();

enQueue(7);
display();

// Fails to enqueue because front == rear + 1


enQueue(8);

return 0;
}

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