Coding Corner: Data Structures - C Program to implement queue operations using an array

Queue is a data structure , similar to Stack , but here in queue we have openings at both the ends , one for insertion and other for deletion.

Some of the common operations of queue are :

Adding an item to queue(enqueue)
Removing an item from a queue(dequeue)
Overflow Condition(Queue full)
Underflow Condition(Queue empty)
Getting the front element(peek)

Overflow situation occur when the queue is full and then we are trying to insert/add another item to the queue .

Underflow situation occur when the queue is empty and the we are trying to remove/delete an item from the queue.

The principle of queue is First In First Out (FIFO).

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PROGRAM :

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int rear = -1,front = -1,item,MAX ,choice ,i;
    printf("Enter Size of Queue : \t ");
    scanf("%d" , &MAX);
    int QueueArray[MAX];
    while (1)
    {
        printf("\nQueue Operations  :");
        printf("\n1. Insert/Add");
        printf("\n2. Remove/Delete");
        printf("\n3. Peek/Front item");
        printf("\n4. Display Queue");
        printf("\n5. Exit");
        printf("\nEnter your choice :\t");
        scanf("%d" , &choice);
        switch (choice)
        {
        case 1:
            if (rear == MAX - 1)
            {
                printf("Queue Overflow \n");
            }
            else
            {
                if (front == -1)
                {
                    front = 0;
                }
                printf("Inset the element in queue : \t");
                scanf("%d" , &item);
                rear = rear + 1;
                QueueArray[rear] = item;
            }

            break;
        case 2:

            if (front == -1 || front > rear)
            {
                printf("Queue Underflow \n");
                break;
            }
            else
            {
                printf("Element deleted from queue is %d \n" , QueueArray[front] );
                front = front + 1;
            }
            break;
        case 3:
            if (front == -1 || front > rear)
            {
                printf("Queue Underflow \n");
                break;
            }
            else
            {
                printf("The front element is : %d \t" , QueueArray[front]);
            }
            break;
        case 4:
            if (front == -1 || front > rear)
            {
                printf("Queue Underflow \n");
                break;
            }
            else
            {
                printf("The current elements in queuue are :");
                for (i = front; i <= rear; i++)
                {
                    printf("%d " ,QueueArray[i]);
                }
            }
            break;
        case 5:
            return 0;
            break;
        default:
            printf("Wrong Entry \n ");
            break;
        }

    }
    return 0;
}