STACK & QUEUE USING LIST.c

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

struct node{
	int i;
	struct node *link;
}*top=NULL,*front=NULL,*rear=NULL,*ptr,*n,*tptr;

void stack();
void queue();
void menu();

int main(){
	menu();
	return 0;
			}

void menu(){
    int c;
	printf("\n				MAIN MENU\n");	
	printf("PRESS 1 FOR STACK\nPRESS 2 FOR QUEUE\nPRESS 3 TO EXIT\nYOUR CHOICE: ");	
	scanf("%d",&c);
	switch(c){
		case 1:
			stack();		 
			break;
		case 2:
			queue();
			break;
		case 3:
			return ;
			break;
		default:
			printf("INVALID INPUT\n");
			menu();
	}
     
 }

void stack(){
     int c;
     printf("\n				STACK MENU\n");	
	 printf("PRESS 1 FOR PUSH\nPRESS 2 FOR POP\nPRESS 3 TO DISPLAY\nPRESS 4 TO EXIT TO MIAN MENU\nYOUR CHOICE: ");
	 scanf("%d",&c);
	 switch(c){
			case 1:
				if(top==NULL){
					top= (struct node*)malloc(sizeof(struct node));
					printf("\nEnter Item : ");
					scanf("%d",&top->i);
					top->link = NULL;
				}
				else{
					n= (struct node*)malloc(sizeof(struct node));
					printf("\nEnter Item : ");
					scanf("%d",&n->i);
					n->link = top;
					top = n;
				}
				stack();						
				break;
			case 2:
				ptr = top;
				if(top == NULL){
					printf("\nERROR! STACK IS EMPTY \n");
								}
				else{
					ptr = top;
					if(top == NULL){
					printf("\nERROR LINK IS EMPTY !\n");
						}
					else{
						top = top->link;
						free(ptr);
							}
					printf("POP OPERATION SUCCESS\n");
					}
				stack();						
				break;	
			case 3:
				ptr = top;
				if(top==NULL){
					printf("\nERROR! STACK IS EMPTY \n");;
							}
				else{
					while(ptr!=NULL){
						printf("%d ",ptr->i);
						ptr = ptr->link;
						}
					}

				stack();						
				break;
			case 4:
				menu();						
				break;								
				}
			}

void queue(){
    int c,itm;
	printf("\n				QUEUE MENU\n");	
	printf("PRESS 1 FOR ENQUE\nPRESS 2 FOR DEQUEUE\nPRESS 3 TO DISPLAY\nPRESS 4 TO EXIT TO MIAN MENU\nYOUR CHOICE: ");
	scanf("%d",&c);
	switch(c){
		case 1:
			n= (struct node*)malloc(sizeof(struct node));
			printf("\nEnter Item : ");
			scanf("%d",&n->i);
			n->link==NULL;
			if(front==NULL){
				front=rear=n;				
				}
			else{
				rear->link=n;
				rear=n;
				rear->link=NULL;
				}
			queue();
			break;
		case 2:
			ptr = front;
			if(front == NULL){
				printf("\nERROR! QUEUE IS EMPTY \n");
							}
			else{
				if(front == rear){
					free(front);
					front = rear = NULL;
				}
				else{
				front = front->link;
				free(ptr);
				}
				printf("DEQUEUE OPERATION SUCCESS\n");
				}
			queue();
			break;
		case 3:
      
			ptr = front;
			if(front==NULL){
				printf("\nERROR! QUEUE IS EMPTY \n");
							}
			else{
				while(ptr!=NULL){
					printf("%d ",ptr->i);
					ptr = ptr->link;
							}
				}
			queue();
			break;
		case 4:
			menu();
			break ;
		default:
			printf("INVALID INPUT\n");
			queue();
							
				}
			}