circular_queue.cpp

#include<bits/stdc++.h>
using namespace std;

struct Queue
{

    int rear, front;

    int size;
    int *arr;

    Queue(int s)
    {
       front = rear = -1;
       size = s;
       arr = new int[s];
    }

    void enQueue(int value);
    int deQueue();
    void displayQueue();
};


void Queue::enQueue(int value)
{
    if ((front == 0 && rear == size-1) ||
            (rear == (front-1)%(size-1)))
    {
        printf("\nQueue is Full");
        return;
    }

    else if (front == -1)
    {
        front = rear = 0;
        arr[rear] = value;
    }

    else if (rear == size-1 && front != 0)
    {
        rear = 0;
        arr[rear] = value;
    }

    else
    {
        rear++;
        arr[rear] = value;
    }
}


int Queue::deQueue()
{
    if (front == -1)
    {
        printf("\nQueue is Empty");
        return INT_MIN;
    }

    int data = arr[front];
    arr[front] = -1;
    if (front == rear)
    {
        front = -1;
        rear = -1;
    }
    else if (front == size-1)
        front = 0;
    else
        front++;

    return data;
}


void Queue::displayQueue()
{
    if (front == -1)
    {
        printf("\nQueue is Empty");
        return;
    }
    printf("\nElements in Circular Queue are: ");
    if (rear >= front)
    {
        for (int i = front; i <= rear; i++)
            printf("%d ",arr[i]);
    }
    else
    {
        for (int i = front; i < size; i++)
            printf("%d ", arr[i]);

        for (int i = 0; i <= rear; i++)
            printf("%d ", arr[i]);
    }
}

int main()
{
    Queue q(5);

    q.enQueue(14);
    q.enQueue(22);
    q.enQueue(13);
    q.enQueue(-6);

    q.displayQueue();

    printf("\nDeleted value = %d", q.deQueue());
    printf("\nDeleted value = %d", q.deQueue());

    q.displayQueue();

    q.enQueue(9);
    q.enQueue(20);
    q.enQueue(5);

    q.displayQueue();

    q.enQueue(20);
    return 0;
}