Queue in C using Linked List

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

struct node
{
    int data;
    struct node* next;
};

struct node *front=NULL, *rear=NULL;

void enq();
void deq();
void display();

int main()
{
    int i,p,q;
    while(1)
    {
        printf("***QUEUE*** \n");
        printf("1.Enqueue\n2.Dequeue\n3.Display\n4.Exit \n");
        scanf("%d", &p);
        switch(p)
        {
        case 1:
            enq();
            break;
        case 2:
            deq();
            break;
        case 3:
            display();
            break;
        case 4:
            exit(0);
        }
    }
    return 0;
}

void enq()
{
    struct node *ptr, *preptr;
    int p;
    printf("Enter value to be enqueued. \n");
    scanf("%d", &p);
    if(rear==NULL)
    {
        rear=(struct node*)malloc(sizeof(struct node));
        rear->data=p;
        rear->next=NULL;
        front=rear;
    }
    else
    {
        ptr=(struct node*)malloc(sizeof(struct node));
        ptr->data=p;
        ptr->next=NULL;
        rear->next=ptr;
        rear=ptr;
    }
}

void deq()
{
    struct node *ptr;
    if(front==NULL)
    {
        printf("Queue is empty. \n");
        return;
    }
    else
    {
        printf("The dequeued value is %d \n", front->data);
        ptr=front;
        front=front->next;
        free(ptr);
    }
}

void display()
{
    struct node *ptr;
    ptr=front;
    if(ptr==NULL)
    {
        printf("Queue is empty. \n");
        return;
    }
    else
    {
        while(ptr!=rear)
        {
            printf("%d \n", ptr->data);
            ptr=ptr->next;
        }
        printf("%d \n", ptr->data);
    }
}