//File intstack.cpp

#include <iostream.h>
#include <stdlib.h>       /*exit*/
#include "intstack.h"
#include "pmglobs.h"

stack::stack() {
   top=NULL;
}

stack::~stack() {
   while (!empty())
      pop();
   top=NULL;
}

void stack::display() {
   node* p = top;
   while (p) {
      cout << p->info << " ";
      p = p->next;
   }
   cout << endl;
}

bool stack::empty() const {
   if (top==NULL)
      return true;
   else
      return false;
}

void stack::push(int item) {
   node* p=new node;
   p->info=item;
   p->next=top;
   top=p;
}

int stack::pop() {
   node* p;
   int n;

   if (empty()) {
      cout<<"\n\nSTACK UNDERFLOW!\n\n";
      exit(1);
   } else {
      p=top;
      top=p->next;
      n=p->info;
      delete p;
   }
   return n;
}

int stack::stacktop() const {
   if (empty()) {
      cout<<"\n\nSTACK IS EMPTY!\n\n";
      exit(1);
   }
   return top->info;
}

//B-16