class Stack{ public: // Standard Stack methods Stack(); bool empty() const; Error_code push(const Stack_entry&item); Error_code pop(); Error_code top(Stack_entry &item) const; // Safety features for linked structures ~Stack(); Stack(const Stack &original); void operator =(const Stack &original); protected: Node *top_node; }; bool Stack::empty() const /* Post:Return true if the Stack is empty, otherwise return false. */ { return ; } Stack::Stack() /* Post: The Stack is initialized to be empty. */ { ; } Error_code Stack::top(Stack_entry &item) const /* Post: The top of the Stack is reported in item. If the Stack is empty the method returns underflow; otherwise it returns success. */ { if ( ) return underflow; item = ; return success; }