写个c++小例子

class Rational{
public:
    const Rational operator*( const Rational& rhs);
    Rational(int num);
private:
    int a;
};

Rational::Rational(int num) :a(num)
{
}

const Rational Rational::operator*(const Rational& rhs)
{
    return Rational(this->a * rhs.a);
}

int main()
{
    Rational a();
    Rational b();
    Rational c = a * b;
    return ;
}