#include <iostream>
using namespace std;

class Context;//Forward declaration

class Strategy{
  public:
	virtual void execute(Context* c)=0;
};

class Strategy1: public Strategy{
  public:
	void execute(Context* c);
};

class Strategy2: public Strategy{
  public:
	void execute(Context* c);
};

class Context{
  public:
 	int Counter=10;
  	Strategy* strategy;

	Context(Strategy* s):strategy(s){}

  	void execute();

  	void ChangeStrategy(Strategy* s);
};

inline void Context::execute(){
	strategy->execute(this);
}

inline void Context::ChangeStrategy(Strategy* s){
	strategy = s;
}

void Strategy1::execute(Context* c){
	cout<<"Calling strategy#1"<<endl;
    c->Counter += 1;
}
void Strategy2::execute(Context* c){
	cout<<"Calling strategy#2"<<endl;
    c->Counter -= 1;
}

static Strategy1 strategy1;
static Strategy2 strategy2;

int main(){
    Context context(&strategy1);

    cout<<"1:"<<context.Counter<<endl;
    context.execute();
    cout<<"2:"<<context.Counter<<endl;
    context.execute();
    cout<<"3:"<<context.Counter<<endl;
    context.ChangeStrategy(&strategy2);
    context.execute();
    cout<<"4:"<<context.Counter<<endl;
    return 0;
}