/*PROGRAM TO IMPLEMENT QUEUES USING SINGLY LINKED LIST*/
#include<stdio.h>
#include<conio.h>
#include<alloc.h>
#include<stdlib.h>
#include<process.h>
struct node
   {
    int info;
    struct node *link;
   };
typedef struct node *NODE;
NODE getnode()
  {
   NODE x;
   x=(NODE)malloc(sizeof(struct node));
   if(x==NULL)
     {
     printf("Out of Memory\n");
     exit(0);
     }
   return x;
  }
NODE insert_rear(int item,NODE first)
    {
    NODE temp,cur,prev;
    temp=getnode();
    temp->info=item;
    temp->link=NULL;
    if(first==NULL)
      return temp;

    cur=first;
    while(cur->link!=NULL)
      {
       cur=cur->link;
      }
     cur->link=temp;
    return first;
  }
NODE delete_front(NODE first)
   {
    NODE temp= first;
    if(first == NULL)
     {
     printf("\n Queue Empty\n ");
     getch();
     return first;
     }
    printf(" %d item has been deleted\n",first->info);
    first = first->link;
    free(temp);
    return first;
  }
void display(NODE first)
    {
     NODE temp = first;
     if(first == NULL)
       {
	printf("\n Queue Empty\n ");
	getch();
	return;
       }
      printf("\nThe contents of queue is");
      while(temp != NULL)
	{
	 printf("\n %d ", temp->info);
	 temp = temp->link;
	}
   }
void main()
  {
  int choice,item,pos;
  NODE first=NULL;
  for(;;)
    {
     clrscr();
     printf("\n1:INSERT\n2:DELETE\n3:DISPLAY\n4:QUIT\n");
     printf("\nENTER YOUR CHOICE :");
     scanf ("%d",&choice);
      switch(choice)
	{
	 case 1:
	      printf("Enter the element to be inserted\n");
	      scanf("%d",&item);
	      first=insert_rear(item,first);
	      break;
	 case 2:
	      first=delete_front(first);
	      break;
	 case 3:
	      display(first);
	      break;
	case 4:
	     exit(0);
	default:
	     printf("Invalid input\n");
	  }
		getch();
	}
    }