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

// to create a node for list
struct node
{
    int data;
    struct node *next;
};

// creating front and rear pointers, and assigning null values to them.
struct node*front=NULL, *rear=NULL;

// To enqueue
void enqueue(int val)
{
   //allocating a dynamic memory to the new node
    struct node*new=malloc(sizeof(struct node));
    new->data=val;
    new->next=NULL;
    if(front==NULL && rear==NULL)
    {
        front=rear=new;
    }
    else
    {
        rear->next=new;
        rear=new;
    }
    printf("The element %d has been added to the queue successfully!\n", val);
}

void dequeue()
{
    struct node*temp;
    if(front==NULL)
    printf("The queue is empty!\n");
    else
    printf("The element %d has been removed from the queue successfully!\n", front->data);
    temp=front;
    front=front->next;
    if(front==NULL)
    rear=NULL;
    free(temp);
}

void show()
{
    struct node*temp=front;
    while(temp!=NULL)
    {
        printf("%d ", temp->data);
        temp=temp->next;
    }
}

void main()
{
    int a,n;
    do
    {
        printf("\nEnter 1 to enqueue, 2 to dequeue, 3 for display and 4 for exit\n");
        scanf("%d", &a);
        switch(a)
        {
            case 1 : printf("Enter element to be added\n");
                    scanf("%d", &n);
                    enqueue(n);
                    break;
            case 2 : dequeue();
                    break;
            case 3 : show();
                    break;
            case 4 : printf("Program terminated successfully!\n");
                    break;
            default : printf("Enter valid number!\n");
                        break;
        }
    }
    while(a!=4);
}