A circular queue is an advanced form of a linear queue that overcomes its limitations using a circular approach. This article explains how to implement a circular queue in C using arrays with complete code and logic for INSERT, DELETE, and DISPLAY operations.
What is a Circular Queue?
In a circular queue, the last position is connected back to the first, forming a circle. This allows efficient use of storage by reusing freed space.
Unlike a simple linear queue, a circular queue does not suffer from the problem of wasted memory.
Circular Queue Operations
| Operation | Description |
|---|---|
| INSERT | Adds an element at the rear |
| DELETE | Removes the front element |
| DISPLAY | Shows all elements in the circular order |
C Program: Circular Queue Using Array
#include <stdio.h>
#define SIZE 5
int queue[SIZE];
int front = -1, rear = -1;
void insert(int value) {
if ((front == 0 && rear == SIZE - 1) || (rear == (front - 1 + SIZE) % SIZE)) {
printf("Queue Overflow\n");
return;
} else if (front == -1) { // First element
front = rear = 0;
} else if (rear == SIZE - 1 && front != 0) {
rear = 0;
} else {
rear++;
}
queue[rear] = value;
printf("%d inserted\n", value);
}
void delete() {
if (front == -1) {
printf("Queue Underflow\n");
return;
}
printf("%d deleted\n", queue[front]);
if (front == rear) {
front = rear = -1; // Queue is empty
} else if (front == SIZE - 1) {
front = 0;
} else {
front++;
}
}
void display() {
if (front == -1) {
printf("Queue is empty\n");
return;
}
printf("Queue elements: ");
if (rear >= front) {
for (int i = front; i <= rear; i++)
printf("%d ", queue[i]);
} else {
for (int i = front; i < SIZE; i++)
printf("%d ", queue[i]);
for (int i = 0; i <= rear; i++)
printf("%d ", queue[i]);
}
printf("\n");
}
int main() {
int choice, value;
while (1) {
printf("\n1. INSERT\n2. DELETE\n3. DISPLAY\n4. EXIT\n");
printf("Enter your choice: ");
scanf("%d", &choice);
switch (choice) {
case 1:
printf("Enter value to insert: ");
scanf("%d", &value);
insert(value);
break;
case 2:
delete();
break;
case 3:
display();
break;
case 4:
return 0;
default:
printf("Invalid choice\n");
}
}
}
Output Example
1. INSERT
2. DELETE
3. DISPLAY
4. EXIT
Enter your choice: 1
Enter value to insert: 10
10 inserted
Enter your choice: 1
Enter value to insert: 20
20 inserted
Enter your choice: 3
Queue elements: 10 20
Enter your choice: 2
10 deleted
Enter your choice: 3
Queue elements: 20
Why Use a Circular Queue?
- Efficient memory usage: Reuses empty slots.
- Prevents overflow when elements are removed and space is available.
- Best for buffered data processing, like printer queues, OS scheduling, etc.