// QUEUE
// Program 5 : To implement QUEUE using linked list

#include <stdio.h>
#include <conio.h>

struct Node
{
	int data;
	struct Node *link;
};

struct Node *front = NULL;
struct Node *rear  = NULL;

 int insert(int );
 int delete();
void display();

main()
{
  int x,opn;

  do
  {
    printf("\n\n\t <1>INSERT    <2>DELETE    <3>DISPLAY    <4>EXIT");
    printf("\n\t Enter your option : ");
    scanf("%d",&opn);

    switch(opn)
	{
		case 1:
			printf("\t Enter number to insert : ");
			scanf("%d", &x);
			if( insert(x))
				printf("\n\t ERROR : OVERFLOW !!!");
			printf("\t Press any key to continue ...");
			getch();
			break;
		
		case 2:
			if( front == NULL )
	       		printf("\t ERROR : UNDERFLOW !!!");
	      	else
	       		printf("\t deleted element is : %d", delete());
      		printf("\n\t Press any key to continue ...");
	      	getch();
	      	break;

      	case 3:
			if( front == NULL )
				printf("\n\t QUEUE IS EMPTY");
			else
				display();
			printf("\n\t Press any key to continue ...");
			getch();
			break;
    }
  }while(opn!=4);
}
// end of main

int insert(int x)
{
  struct Node *newNode = malloc(sizeof(struct Node));

  if(newNode == NULL)
   return -1; //overflow

  newNode->data = x;
  newNode->link = NULL;

  if( front == NULL )
   front = newNode;
  else
   rear->link = newNode;

  rear = newNode;
  return 0;
}

int delete()
{
  int x;
  struct Node *tmpNode = front;

  if( front == NULL )
   return -1;

  x = front->data;
  front = front->link;
  free(tmpNode);

  return x;
}

void display()
{
  struct Node *tmpNode = front;

  if(front == NULL)
   return ;

  printf("\n\t QUEUE = [ ");

  for( ; tmpNode != NULL ; tmpNode = tmpNode->link )
   printf(" %d ",tmpNode->data);

  printf("]");
}