Overloading ++ and << >> istream and ostream

[xgiovio]

#include <iostream>
#include <string>

using namespace std;


class persona {

public:
    persona (const string in_nome = "null", const string in_cognome = "null", const int in_eta =0)
    :nome(in_nome), cognome(in_cognome),eta(in_eta){}
    
    void print_nome () const {
        cout << nome << endl;
    }
    
    void print_cognome () const {
        cout << cognome << endl;
    }
    
    void print_eta () const {
        cout << eta << endl;
    }
    
    const string & get_nome () const {
        return nome;
    }
    
    const string & get_cognome () const {
        return cognome;
    }
    
    int & get_eta ()  {
        return eta;
    }
    
    void add_eta (int value){
    
        eta+=value;
    }
    
private:
    const string nome;
    const string cognome;
    int eta;

};


persona operator++(persona & oggetto, int value){ // postfix
    
    persona old(oggetto);
    
    oggetto.add_eta(1);
    
    return old;

}

persona & operator++(persona & oggetto){ ///////// prefix
    
    
    oggetto.add_eta(1);
    
    return oggetto;
    
}



ostream & operator<< (ostream & out, persona & oggetto){

    out << oggetto.get_eta();

    return out;
}

istream & operator>> (istream & in, persona &oggetto){
    int tmp;
    in >> tmp;
    oggetto.add_eta(tmp);

    return in;
}


int main (){
    
    persona obj1; // create object
    cout << (obj1++).get_eta() << endl; // increment but return old value - postfix
    cout << (obj1).get_eta() << endl; // new value avaible now - postfix
    cout << (++obj1).get_eta() << endl; // new value avaible immediately - prefix
    
    ///// testing << overloading

    cout << obj1 << endl;
    
    /// tesing >> overloading
    
    cin >> obj1 ;
    cout << obj1;
    
    
    
    return 0;


}