наследование ( с новой фунуцией)

// наследование.cpp: определяет точку входа для консольного приложения.
//

#include "stdafx.h"

#include <iostream>

using namespace std;


class Rational {
private:
    int chis, znam;
public:
    Rational() {
        chis = 0; znam = 1;
    }

    Rational(int x) {
        chis = x; znam = 1;
    }

    Rational(int c, int z) {
        chis = c; znam = z;
    }

    Rational(const char *str) {
        chis = 0;
        znam = 1;
        sscanf(str, "%d / %d", &chis, &znam);
    }

    int get_chis() const {
        return chis;
    }

    int get_znam() const {
        return znam;
    }
    double approx() {
        return get_chis()/double(get_znam());
    }

    friend double approx(Rational r);
};


class MegaRational: public Rational {
public:
    MegaRational(): Rational()
    {
    }

    MegaRational(int x): Rational(x)
    {
    }

    MegaRational(int c, int z): Rational(c, z)
    {
    }

    MegaRational(const char *str) : Rational(str)
    {
    }

    void drob(Rational a) {
        if(a.get_chis() > a.get_znam()) {
            cout << "B = " << a.get_chis() / a.get_znam() << " и " << a.get_chis()/double(a.get_znam()) <<endl;
        }
        else
            cout << "C = " << a.get_chis() % a.get_znam()<< endl;
    }
};

double approx(Rational r) {
    return r.chis/double(r.znam);
}


Rational operator+(Rational a, Rational b) {
    Rational res(a.get_chis()*b.get_znam() + a.get_znam()*b.get_chis(),
                 a.get_znam()*b.get_znam());
    return res;
}

Rational operator-(Rational a, Rational b) {
    Rational res(a.get_chis() * b.get_znam() - b.get_chis() * a.get_znam(),
                 a.get_znam() * b.get_znam());
    return res;
}

Rational operator*(Rational a, Rational b) {
    Rational res(a.get_chis() * b.get_chis(),
                 a.get_znam() * b.get_znam());
    return res;
}

Rational operator/(Rational a, Rational b) {
    Rational res(a.get_chis() * b.get_znam(),
        a.get_znam() * b.get_chis());
    return res;
}


ostream& operator<<(ostream& o, Rational r) {
    o << r.get_chis() << " / " << r.get_znam();
    return o;
}


int _tmain(int argc, _TCHAR* argv[])
{
    Rational     r1(1, 5),
                 r2(4, 8),
                 r3(4);
    MegaRational r4(3, 2),
                 r5("2/7");

    Rational a = operator+(r1, r2);
    Rational b = operator-(r1, r5);
    Rational c = operator*(r2, r3);
    Rational d = operator/(r5, r2);

    cout << " r1 = " << r1 << endl;
    cout << " r2 = " << r2 << endl;
    cout << " r3 = " << r3 << endl;
    cout << " r4 = " << r4 << endl;
    cout << " r5 = " << r5 << endl;

    cout << endl;

    Rational res = r1 + r2;
    cout << " a = " << a.approx() << " = " << res << endl;
    cout << " b = " << b.approx() << " = " << r1 - r5 << endl;
    cout << " c = " << c.approx() << " = " << r2 * r3 << endl;
    cout << " d = " << d.approx() << " = " << r5 / r2 << endl;

    cout << endl;
    cout << " r4 = " << r4.drob() << " = " << r4 << endl;

    return 0;
}