C program to implement queue using array (linear implementation of queue in C)

Linear implementation of queue in C: In this tutorial, we will learn how to implement a queue using an array using the C program? By IncludeHelp Last updated : August 10, 2023

QUEUE is a simple data structure, which has FIFO ( First In First Out) property in which Items are removed in the same order as they are entered.

QUEUE has two pointer FRONT and REAR, Item can be pushed by REAR End and can be removed by FRONT End.

Problem statement

Write a C program to implement a queue using an array with the various queue operations such as INSERT, REMOVE, and DISPLAY.

C program to implement queue using array

#include <stdio.h>
#define MAX 10

int QUEUE[MAX], front = -1, rear = -1;

/** function        :   insert_in_Q(),
to push an item into queue.
**/
void insert_in_Q(int queue[], int ele)
{
    if (rear == -1) {
        front = rear = 0;
        queue[rear] = ele;
    }
    else if (rear == MAX - 1) {
        printf("\nQUEUE is full.\n");
        return;
    }
    else {
        rear++;
        queue[rear] = ele;
    }
    printf("\nItem inserted..");
}

/** function    :   display_Q(),
to display queue elements
**/

void display_Q(int queue[])
{
    int i;
    if (rear == -1) {
        printf("\nQUEUE is Empty.");
        return;
    }
    for (i = front; i <= rear; i++) {
        printf("%d,", queue[i]);
    }
}

/** function    :   remove_from_Q(),
to remove (pop) an item from queue.
**/
void remove_from_Q(int queue[])
{
    int ele;
    if (front == -1) {
        printf("QUEUE is Empty.");
        return;
    }
    else if (front == rear) {
        ele = queue[front];
        front = rear = -1;
    }
    else {
        ele = queue[front];
        front++;
    }
    printf("\nItem removed : %d.", ele);
}

int main()
{
    int ele, choice;
    while (1) {
        //clrscr();
        printf("\nQUEUE Elements are : ");
        display_Q(QUEUE);
        printf("\n\nEnter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): ");
        scanf("%d", &choice);
        switch (choice) {
        case 0:
            return 0;
            break;
        case 1:
            printf("Enter an element to insert: ");
            scanf("%d", &ele);
            insert_in_Q(QUEUE, ele);
            break;
        case 2:
            display_Q(QUEUE);
            break;
        case 3:
            remove_from_Q(QUEUE);
            break;
        default:
            printf("\nInvalid choice\n");
            break;
        }

    } //end of while(1)
    return 0;
}

Output

QUEUE Elements are : 
QUEUE is Empty.

Enter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): 1
Enter an element to insert: 10

Item inserted..
QUEUE Elements are : 10,

Enter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): 1
Enter an element to insert: 20

Item inserted..
QUEUE Elements are : 10,20,

Enter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): 3

Item removed : 10.
QUEUE Elements are : 20,

Enter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): 2
20,
QUEUE Elements are : 20,

Enter choice (1:Insert, 2:Display, 3:Remove, 0:Exit): 0