read_rational

std::istream& Rational::readFrom(std::istream& istrm) {
    char slash(0);
    int num(0), den(1);
    if (istrm.good()) {
        istrm >> num >> slash >> den;
        if (slash == '/') {
            if (den == 0) throw std::invalid_argument("Denominator cannot be equal to zero!");
            numerator = num;
            denominator = den;
            Simplify();
        }
        else {
            istrm.setstate(std::ios_base::failbit);
        }
    }
    return istrm;
}