// Prog: stack.h
// definition of the class ifmp::stack
#include <ostream>

namespace ifmp {

  // linked list node
  struct list_node {
    int               key;
    list_node* next;
    list_node (int k, list_node* n = 0) 
    : key (k), next (n) {}
  };
  
  class stack {
  public:
    // default constructor: 
    // POST: *this is an empty stack
    stack();  

    // destructor
    ~stack();

    // copy constructor
    stack (const stack& s);

    // assignment operator
    stack& operator= (const stack& s); 

    // POST: key is pushed onto *this
    void push (int key);

    // POST: returns whether *this is empty 
    bool empty () const;

    // PRE: !empty()
    // POST: top element of *this is returned
    int top () const; 

    // PRE: !empty()
    // POST: top element of *this is popped from *this
    void pop (); 

    // POST: *this is written to o
    void print (std::ostream& o) const; 

  private:
    list_node* top_node;

    // PRE:  to == 0
    // POST: nodes after from are copied to nodes after to
    void copy (const list_node* from, list_node*& to);

    // POST: nodes after from are deleted
    void clear (list_node* from);
  };

  // output operator
  std::ostream& operator<< (std::ostream& o, const stack& l);

} // end namespace