// STACK
// Program 2 : To implement stack using linked list

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

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

struct Node *top = NULL;

 int push(int );
 int pop ();
void show();

main()
{
	int x,opn;
	do
	{
    		printf("\n\n\t <1>PUSH    <2>POP    <3>SHOW    <4>EXIT");
    		printf("\n\t Enter your option : ");
    		scanf("%d", &opn);
	
    		switch(opn)
    		{
      			case 1: printf("\t Enter number to push : ");
	      			scanf("%d", &x);
	      			if( push(x))
	       				printf("\n\t ERROR : OVERFLOW !!!");
	      			printf("\t Press any key to continue ...\n");
	      			getch();
	      			break;

      			case 2: if( top == NULL)
	       				printf("\n\t ERROR : UNDERFLOW !!!");
	      			else
	       				printf("\t poped number is : %d ", pop());
	      			printf("\t Press any key to continue ...\n");
	      			getch();
	      			break;

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

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

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

  	newNode->data = x;
  	newNode->link = top;
  	top = newNode;
  	return 0;
}

int pop ()
{
	int x;
  	struct Node *tmpNode = top;

  	if(top == NULL)
   		return -1;

  	x = top->data;
  	top = top->link;
  	free(tmpNode);
  	return x;
}

void show (  )
{
	struct Node *tmpNode = top;
	
	if(top == NULL)
   		return ;

  	printf("\t STACK = [ ");
  	for( ; tmpNode != NULL ; tmpNode = tmpNode->link )
   		printf(" %d ",tmpNode->data);
  	printf("]");
}