Program dengan stack

#include <iostream.h>
#include <conio.h>
#define namespace std;

const int STACK_SIZE = 100;

class stack {
     private:
          int count;
          int data[STACK_SIZE];
     public:
          stack();
          ~stack();
          void push(const int item);
          int pop(void);
     };
stack::stack()
{
     count = 0;
}
stack::~stack() {}
void stack::push(const int item)
{
     if (count < STACK_SIZE)
     {
          data[count] = item;
          ++count;
     }
     else cout << "Overflow!\n";
}
int stack::pop(void)
{
     if (count >0)
     {
          --count;
          return (data[count]);
     }
     else
     {
          cout << "Underflow!\n";
          return 0;
     }
}
int menu();

class number
{
     public:
          number() {x=0;}
          number (int num){x=num;}
          virtual ~number() {}
          virtual void print_it()=0;
          int num;
     private:
     int x;
};