#include<iostream>
 #include<cassert>
 #include<cmath>
  using namespace std;

   typedef int stack_type;

   class stack
    {
     public:
      stack();
      bool empty();
      void psh(stack_type);
      stack_type pop();
     private:
      struct stacknode
       {
        stack_type item;
        struct stacknode*next;
       };
      stacknode*top;
    };

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

  bool stack::empty()
   {
    return !top;
   }

  void stack::psh(stack_type newitem)
   {
    stacknode*newnode;
    newnode = new stacknode;
    newnode->item = newitem;
    newnode->next = top;
    top = newnode;
   }

  stack_type stack::pop()
   {
    assert(top);
    int result = top->item;
    top = top->next;
    return result;
   }

  int main()
   {
    stack S=stack();
    S.psh(4);
    S.psh(3);
    S.psh(6);
    cout << "pop() returns " << S.pop() << endl;
    S.psh(5);
    while(!S.empty())
     cout << S.pop() << endl;
    return 0;
   }