Queue Using Doubly

#include <stdio.h>
#include <stdlib.h>
struct node
{
    int id;
    struct node *next,*prev;
}*start=NULL,*end=NULL,*current;
int co,i;
void cre()
{
    struct node *n;
    if(start==NULL)
    {
        printf("\nEnter Value:");
        n=(struct node*)malloc(1*sizeof(struct node));
        n->next=NULL;
        n->prev=NULL;
        scanf("%d",&n->id);
        start=n;
        end=n;
        current=n;
        co++;
    }
    else
    {
        printf("\nEnter Value:");
        n=(struct node*)malloc(1*sizeof(struct node));
        n->next=NULL;
        n->prev=NULL;
        scanf("%d",&n->id);
        current->next=n;
        n->prev=current;
        end=n;
        current=n;
        co++;
    }
}
void del()
{
    if(co==1)
    {
        start=NULL;
        end=NULL;
    }
    if(start==NULL && end==NULL)
    {
        printf("\nQueue is Empty.\n");
    }
    else
    {
        struct node *c,*t;
        c=start;
        t=c->next;
        t->prev=NULL;
        start=t;
        co--;
    }

}
void dis()
{
    if(start==NULL && end==NULL)
    {
        printf("\nQueue is Empty.\n");
    }
    else
    {
        struct node *c;
        c=start;
        while(c!=NULL)
        {
            printf("%d-->",c->id);
            c=c->next;
        }
        printf("NULL\n");
        printf("Front : %d Rear : %d\n",start->id,end->id);
    }
}
int main()
{
    int x;
    printf("Enter the value of Queue\n");
    scanf("%d",&i);
    while(1)
    {
        printf("1.Ins, 2.Del,3.Dis\n");
        scanf("%d",&x);
        switch(x)
        {
        case 1:
            {
                if(co==i)
                {
                    printf("Queue is Full.\n");
                    break;
                }
                else
                {
                    cre();
                    break;
                }
            }
        case 2:
            {
                del();
                break;
            }
        case 3:
            {
                dis();
                break;
            }
        }
    }
}