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#include <iostream>

using namespace std;

class State;

class ConcreteStateB;

class ConcreteStateA;

class State {

public:

virtual void OperationChangeState(Context*) = 0;

virtual void OperationInterface(Context*) = 0;

virtual ~State() { }

protected:

bool ChangeState(Context* con, State *st) {

con->ChangeState(st);

}

};

class ConcreteStateA :public State {

public:

void OperationChangeState(Context* con) {

OperationInterface(con);

this->ChangeState(con, new ConcreteStateB());

}

void OperationInterface(Context* con) {

cout << "ConcreteStateA::OperationInterface..." << endl;

}

};

class ConcreteStateB :public State {

public:

void OperationChangeState(Context* con) {

OperationInterface(con);

this->ChangeState(con, new ConcreteStateA());

}

void OperationInterface(Context* con) {

cout << "ConcreteStateB::OperationInterface..." << endl;

}

};

class Context {

public:

Context(State* st) {

_st = st;

}

void OperationInterface() {

_st->OperationInterface(this);

}

void OperationChangeState() {

_st->OperationInterface(this);

}

private:

friend class State;

bool ChangeState(State* st) {

_st = st;

return true;

}

State *_st;

};

int main() {

State *st = new ConcreteStateA();

Context *con = new Context(st);

con->OperationInterface();

con->OperationInterface();

con->OperationInterface();

delete con;

delete st;

return 0;

}