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

struct node
{
    int info;
    struct node *ptr;
}*front,*rear,*temp,*front1;

int frontelement();
void enq(int data);
void deq();
void empty();
void display();
void create();
void queuesize();

int count = 0;

void main()
{
    int no, ch, e;
    printf("\n 1 - Enque");
    printf("\n 2 - Deque");
    printf("\n 3 - Front element");
    printf("\n 4 - Empty");
    printf("\n 5 - Exit");
    printf("\n 6 - Display");
    printf("\n 7 - Queue size");
    create();
    while (1)
    {
            printf("\n Enter choice : ");
            scanf("%d", &ch);
            switch (ch)
            {
                    case 1:
                    printf("Enter data : ");
                    scanf("%d", &no);
                    enq(no);
                    break;

                    case 2:
                    deq();
                    break;

                    case 3:
                    e = frontelement();
                    if (e != 0)
                        printf("Front element : %d", e);
                    else
                        printf("\n No front element in Queue as queue is empty");
                    break;

                    case 4:
                    empty();
                    break;

                    case 5:
                    exit(0);

                    case 6:
                    display();
                    break;

                    case 7:
                    queuesize();
                    break;

                    default:
                        printf("Wrong choice, Please enter correct choice  ");
                    break;
            }
    }
}

/* Create an empty queue */
void create()
{
        front = rear = NULL;
}

/* Returns queue size */
void queuesize()
{
        printf("\n Queue size : %d", count);
}

/* Enqueing the queue */
void enq(int data)
{
    if (rear == NULL)
    {
            rear = (struct node *)malloc(1*sizeof(struct node));
            rear->ptr = NULL;
            rear->info = data;
            front = rear;
    }
    else
    {
            temp=(struct node *)malloc(1*sizeof(struct node));
            rear->ptr = temp;
            temp->info = data;
            temp->ptr = NULL;

            rear = temp;
    }
    count++;
}

/* Displaying the queue elements */
void display()
{
    front1 = front;

    if ((front1 == NULL) && (rear == NULL))
    {
        printf("Queue is empty");
        return;
    }
    while (front1 != rear)
    {
        printf("%d ", front1->info);
        front1 = front1->ptr;
    }
    if (front1 == rear)
        printf("%d", front1->info);
}

/* Dequeing the queue */
void deq()
{
    front1 = front;

    if (front1 == NULL)
    {
            printf("\n Error: Trying to display elements from empty queue");
            return;
    }
    else
        if (front1->ptr != NULL)
        {
            front1 = front1->ptr;
            printf("\n Dequed value : %d", front->info);
            free(front);
            front = front1;
        }
        else
        {
            printf("\n Dequed value : %d", front->info);
            free(front);
            front = NULL;
            rear = NULL;
        }
        count--;
    }

/* Returns the front element of queue */
int frontelement()
{
    if ((front != NULL) && (rear != NULL))
        return(front->info);
    else
        return 0;
}

/* Display if queue is empty or not */
void empty()
{
     if ((front == NULL) && (rear == NULL))
        printf("\n Queue empty");
    else
       printf("Queue not empty");
}