Program 11 - Input Restricted Double Ended Queue

	#include <stdio.h>
	#include <stdlib.h>
	struct node {
	int data;
	struct node *next;
	};
	struct node *start = NULL, *last = NULL;
	void create(){
	struct node *nn;
	int num;
	printf("Enter data or enter -1 to stop: ");
	scanf("%d", &num);
	while(num != -1) {
	nn = (struct node *) malloc(sizeof(struct node));
	nn -> data = num;
	nn -> next = NULL;
	if(start == NULL) {
	start = last = nn;
	} else {
	last -> next = nn;
	last = nn;
	}
	printf("Enter data or enter -1 to stop: ");
	scanf("%d", &num);
	}
	}
	void insert_end(int num){
	struct node *nn;
	nn = (struct node *) malloc(sizeof(struct node));
	nn -> data = num;
	nn -> next = NULL;
	if(start == NULL) {
	start = last = nn;
	} else {
	last -> next = nn;
	last = nn;
	}
	}
	void delete_beg() {
	struct node *p;
	if(start == NULL) {
	printf("Deque Empty\n");
	} else {
	p = start;
	start = start -> next;
	free(p);
	}
	}
	void delete_end(){
	struct node *p, *q;
	if(start == NULL) {
	printf("Deque Empty\n");
	} else if(start -> next == NULL) {
	//Only one node
	free(start);
	start = last = NULL;
	} else {
	p = start;
	q = NULL;
	while(p -> next != NULL) {
	q = p;
	p = p -> next;
	}
	last = q;
	last -> next = NULL;
	free(p);
	}
	}
	void display(){
	struct node *p;
	if(start == NULL) {
	printf("Deque Empty\n");
	} else {
	printf("The deque is: \n");
	p = start;
	while(p != NULL) {
	printf("%d ", p -> data);
	p = p -> next;
	}
	}
	printf("\n");
	}
	int main(){
	int choice, num, rpt = 1;
	printf("***Create Double Ended Queue\n");
	create();
	while(rpt != 0){
	printf("1. Insert at End\n2. Delete from Beginning\n3. Delete from End\n4. Display\n5. Exit\n");
	printf("--------------\n");
	printf("Enter a choice: ");
	scanf("%d", &choice);
	switch(choice){
	case 1:
	printf("Enter num: ");
	scanf("%d", &num);
	insert_end(num);
	display();
	break;
	case 2:
	delete_beg();
	display();
	break;
	case 3:
	delete_end();
	display();
	break;
	case 4:
	display();
	break;
	case 5:
	exit(0);
	}
	printf("Do you want to continue? (1/0): ");
	scanf("%d", &rpt);
	system("cls");
	}
	}