stack template

template <class T>
class Stack;
template <class T>
class Node{
  T _data;
  Node<T>* _next;
  Node(T data, Node<T>* next);
  friend class Stack<T>;
};
template <class T>
class Stack{
  Node<T>* _top;
public:
  Stack(void);
  virtual ~Stack(void);
  void push(T data);
  T pop(void);
  bool isEmpty(void);
};

template <class T>
Node<T>::Node(T data, Node<T>* next){
  _data = data;  // T must be ok with operator =
  _next = next;
}

template <class T>
Stack<T>::Stack(void){
  _top = (Node<T>*)0;
}
template <class T>
Stack<T>::~Stack(void){
  Node<T>* toDel;
  while(_top){
    toDel = _top;
    _top = _top->_next;
    delete toDel;
  }
}

template <class T>
void Stack<T>::push(T data){
  Node<T>* tempnode = new Node<T>(data, _top);
  _top = tempnode;
}
template <class T>
T Stack<T>::pop(void){
  T ret = _top->_data; // T needs should be ok with copying
  Node<T>* toDel = _top;
  _top = _top->_next;
  delete toDel;
  return ret;
}
template <class T>
bool Stack<T>::isEmpty(void){
  return _top == (Node<T>*)0;
}