#ifndef STACK_H
#define STACK_H

//abstract Stack class
template <class Elem> class Stack {
public:
  // Reinitialize the stack
  virtual void clear() = 0;
  // Push an element onto the top of the stack.
  virtual bool push(const Elem&) = 0;
  // Remove the element at the top of the stack. 
  virtual bool pop() = 0;
  // Get a copy of the top element in the stack
  virtual bool topValue(Elem&) const = 0;
  // Return the number of elements in the stack.
};

#endif