std::ostream & operator<<(std::ostream &os, const Complexe &c) {
    return os << c.getReel() << ' ' << c.getImg();
}

Complexe operator-(const Complexe &c1, const Complexe &c2) {
    return Complexe(c1.getReel() - c2.getReel(),
                    c1.getImg() - c2.getImg());
}