Queue Implementation in C Using Array with INSERT, DELETE, DISPLAY Operations

A queue is a linear data structure that follows the First In First Out (FIFO) principle. That means the element inserted first is removed first. This blog explains how to implement a queue in C using arrays with the operations: INSERT, DELETE, and DISPLAY.

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What is a Queue?

A queue works like a line at a bank or ticket counter:

• The first person to enter the line is the first one to be served.
• New elements are inserted at the rear.
• Elements are removed from the front.

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Queue Operations

Operation	Description
INSERT	Adds an element to the rear of the queue
DELETE	Removes an element from the front
DISPLAY	Shows all elements in the queue

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C Program: Queue Using Arrays

#include <stdio.h>
#define SIZE 100

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

// INSERT operation
void insert(int value) {
    if (rear == SIZE - 1) {
        printf("Queue Overflow\n");
    } else {
        if (front == -1) front = 0;
        rear++;
        queue[rear] = value;
        printf("%d inserted into queue\n", value);
    }
}

// DELETE operation
void delete() {
    if (front == -1 || front > rear) {
        printf("Queue Underflow\n");
    } else {
        printf("%d deleted from queue\n", queue[front]);
        front++;
    }
}

// DISPLAY operation
void display() {
    if (front == -1 || front > rear) {
        printf("Queue is empty\n");
    } else {
        printf("Queue elements: ");
        for (int i = front; 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");
        }
    }
}

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Sample Output

1. INSERT
2. DELETE
3. DISPLAY
4. EXIT

Enter your choice: 1
Enter value to insert: 10
10 inserted into queue

Enter your choice: 1
Enter value to insert: 20
20 inserted into queue

Enter your choice: 3
Queue elements: 10 20

Enter your choice: 2
10 deleted from queue

Enter your choice: 3
Queue elements: 20

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Key Notes

• Queue follows FIFO: First In First Out.
• Overflow occurs if the array is full.
• Underflow occurs if there’s nothing left to delete.