#include <iostream>
using namespace std;

//Handler
class Rescuer {
protected:
    Rescuer* next = NULL;
    int code;

    virtual void toHelp() = 0;

public:
    //HandleRequest()
    void help(int code) {
        if (this->code == code) {
            toHelp();
        } else if (next != NULL) {
            next->help(code);
        }
    }
};

//ConcreteHandler
class Firefighter: public Rescuer {
public:
    Firefighter(Rescuer* next) {
        this->next = next;
        this->code = 1;
    }

protected:
    void toHelp() {
        cout << "call firefighters\n";
    }
};

//ConcreteHandler
class Police: public Rescuer {
public:
    Police(Rescuer* next) {
        this->next = next;
        this->code = 2;
    }

protected:
    void toHelp() {
        cout << "call the police\n";
    }
};

//ConcreteHandler
class Ambulance: public Rescuer {
public:
    Ambulance(Rescuer* next) {
        this->next = next;
        this->code = 3;
    }

protected:
    void toHelp() {
        cout << "call an ambulance\n";
    }
};

Ambulance ambulance(NULL);
Police police(&ambulance);
Firefighter firefighter(&police);
firefighter.help(1);
//printed: call firefighters
firefighter.help(2);
//printed: call the police
firefighter.help(3);
//printed: call an ambulance