Calculator Week4 Exception

#include <iostream>
#include <string>

class Rational
{
public:
    Rational()
    {
        _numerator = 0;
        _denominator = 1;
    }
    Rational(const int numerator, const int denominator)
    {
        if (denominator == 0)
        {
            throw std::exception("Invalid argument");
        }

        int GCD = FindGCD(numerator, denominator);

        if (numerator > 0 && denominator < 0 || numerator < 0 && denominator < 0)
        {
            _numerator = -numerator / GCD;
            _denominator = -denominator / GCD;
        }
        else
        {
            _numerator = numerator / GCD;
            _denominator = denominator / GCD;
        }
    }

    int GetNumerator() const
    {
        return _numerator;
    }

    int GetDenominator() const
    {
        return _denominator;
    }

private:
    int _numerator;
    int _denominator;

    int FindGCD(int numerator, int denominator)
    {
        numerator = abs(numerator);
        denominator = abs(denominator);

        while (numerator > 0 && denominator > 0)
        {
            if (numerator > denominator)
            {
                numerator %= denominator;
            }
            else
            {
                denominator %= numerator;
            }
        }

        return numerator + denominator;
    }
};

Rational operator+ (const Rational& lhs, const Rational& rhs)
{
    if (lhs.GetDenominator() == rhs.GetDenominator())
        return { lhs.GetNumerator() + rhs.GetNumerator(), lhs.GetDenominator() };

    return { lhs.GetNumerator() * rhs.GetDenominator() + rhs.GetNumerator() * lhs.GetDenominator(), lhs.GetDenominator() *rhs.GetDenominator() };
}

Rational operator- (const Rational& lhs, const Rational& rhs)
{
    if (lhs.GetDenominator() == rhs.GetDenominator())
        return { lhs.GetNumerator() - rhs.GetNumerator(), lhs.GetDenominator() };

    return { lhs.GetNumerator() * rhs.GetDenominator() - rhs.GetNumerator() * lhs.GetDenominator(), lhs.GetDenominator() * rhs.GetDenominator() };
}

Rational operator* (const Rational& lhs, const Rational& rhs)
{
    return { lhs.GetNumerator() * rhs.GetNumerator(), lhs.GetDenominator() * rhs.GetDenominator() };
}

Rational operator/ (const Rational& lhs, const Rational& rhs)
{
    const int numerator = lhs.GetNumerator() * rhs.GetDenominator();
    const int denominator = rhs.GetNumerator() * lhs.GetDenominator();

    if (denominator == 0)
        throw std::exception("Division by zero");

    return { numerator, denominator };
}

std::istream& operator>> (std::istream& stream, Rational& obj)
{
    if(stream.good())
    {
        int numerator = 0;
        int denominator = 0;
        stream >> numerator;
        if (stream.peek() != '/')
            throw std::exception("/");
        stream.ignore(1);
        stream >> denominator;

        obj = { numerator, denominator };
    }

    return stream;
}

std::ostream& operator<< (std::ostream& stream, Rational& obj)
{
    stream << obj.GetNumerator() << "/" << obj.GetDenominator();

    return stream;
}

int main()
{
    try
    {
        Rational r1, r2;
        char oper;

        std::cin >> r1 >> oper >> r2;

        if(oper == '+')
        {
            Rational result = r1 + r2;
            std::cout << result << std::endl;
        }
        else if(oper == '-')
        {
            Rational result = r1 - r2;
            std::cout << result << std::endl;
        }
        else if(oper == '*')
        {
            Rational result = r1 * r2;
            std::cout << result << std::endl;
        }
        else if(oper=='/')
        {
            Rational result = r1 / r2;
            std::cout << result << std::endl;
        }
    }
    catch (std::exception& ex)
    {
        std::cout << ex.what() << std::endl;
    }
}