#include <iostream>
using namespace std;

class Number;

class Memento{
    friend class Number; 
    int _state;  
  public:
    Memento(int val){
        _state = val;
    }
};

class Number{
    int _value;
  public:
    Number(int value){
        _value = value;
    }
    void dubble(){
        _value *= 2;
    }
    void half(){
        _value /= 2;
    }
    int getValue(){
        return _value;
    }
    Memento *createMemento(){
        return new Memento(_value);
    }
    void reinstateMemento(Memento *mem){
        _value = mem->_state;
    }
};

class Command{
  public:
    typedef void(Number:: *Action)();
    Command(Number *receiver, Action action){
        _receiver = receiver;
        _action = action;
    }
    virtual void execute(){
        _mementoList[_numCommands] = _receiver->createMemento();
        _commandList[_numCommands] = this;
        if (_numCommands > _highWater)
          _highWater = _numCommands;
        _numCommands++;
        (_receiver->*_action)();
    }
    static void undo(){
        if (_numCommands == 0){
            cout << "*** Attempt to run off the end!! ***" << endl;
            return ;
        }
        _commandList[_numCommands - 1]->_receiver->reinstateMemento
          (_mementoList[_numCommands - 1]);
        _numCommands--;
    }
    void static redo(){
        if (_numCommands > _highWater){
            cout << "*** Attempt to run off the end!! ***" << endl;
            return ;
        }
        (_commandList[_numCommands]->_receiver->*(_commandList[_numCommands]
          ->_action))();
        _numCommands++;
    }
  protected:
    Number *_receiver;
    Action _action;
    static Command *_commandList[20];
    static Memento *_mementoList[20];
    static int _numCommands;
    static int _highWater;
};

Command *Command::_commandList[];
Memento *Command::_mementoList[];
int Command::_numCommands = 0;
int Command::_highWater = 0;

int main(){
  int i;
  cout << "Integer: ";
  cin >> i;
  Number *object = new Number(i);
  Command *commands[3];
  commands[1] = new Command(object, &Number::dubble);
  commands[2] = new Command(object, &Number::half);
  while (true){
  	cout << "0:Exit\n1:Double\n2:Half\n3:Undo\n4:Redo\n>>>";
  	cin >> i;
  	if (i==0) break;
    switch(i){
		case 3: Command::undo(); break;
    	case 4: Command::redo(); break;
    	default: commands[i]->execute();
    }
    cout << "Object Value is " << object->getValue() << endl;
  }
  return 0;
}