#include <iostream>

using namespace std;

class Context;

class State {
public:
 virtual void Handle(Context* c) = 0;
};

class Context {
private:
 State* m_state;
public:
 Context(State* p):
 m_state(p) {
 }
 void Request() {
 if (m_state != NULL) {
 m_state->Handle(this);
 }
 }
 void changeState(State* s) {
 if (m_state != NULL) {
 delete m_state;
 m_state = NULL;
 }
 m_state = s;
 }
};


class ConcretStateA: public State {
public:
 void Handle(Context* c);
};


class ConcretStateB: public State {
public:
 void Handle(Context* c);
};

void ConcretStateA::Handle(Context* c) {
 cout << "Handle by ConcretStateA" << endl;
 if (c != NULL) {
 c->changeState(new ConcretStateB());
 }
}


void ConcretStateB::Handle(Context* c) {
 cout << "Handle by ConcretStateB" << endl;
 if (c != NULL) {
 c->changeState(new ConcretStateA());
 }
}

int main(int argc, char** argv) {
 Context* c = new Context(new ConcretStateA());
 c->Request();
 c->Request();
 c->Request();
 c->Request();
 c->Request();
 c->Request();
 
}