Overload

#include <iostream>

using namespace std;

struct Rational
{
    Rational(int numerator = 0, int denominator = 1)
            :numerator_(numerator), denominator_(denominator){};

    void add(Rational rational){
        this->numerator_ += (rational.numerator_ * this->denominator_);
    };
    void sub(Rational rational){
        this->numerator_ -= (rational.numerator_ * this->denominator_);
    };
    void mul(Rational rational);
    void div(Rational rational);

    void neg(){
        this->numerator_  = -this->numerator_;
    };
    void inv();
    double to_double() const{
        return (double)numerator_/(double)denominator_;
    };
    
    Rational& operator+=(const Rational rat){
        this->add(rat);
        return (*this);
    }
    
    Rational& operator+=(const int rat){
        Rational r1;
        r1.numerator_ = rat;
        r1.denominator_ = 1;
        (*this) += r1;
        return (*this);
    }
    
    Rational& operator-=(const Rational rat){
        this->sub(rat);
        return (*this);
    }
    
    Rational& operator-=(const int rat){
        Rational r1;
        r1.numerator_ = rat;
        r1.denominator_ = 1;
        (*this) -= r1;
        return (*this);
    }
    
    Rational& operator*=(const Rational rat){
        this->mul(rat);
        return (*this);
    }
       
    Rational& operator*=(const int rat){
        Rational r1;
        r1.numerator_ = rat;
        r1.denominator_ = 1;
        (*this) *= r1;
        return (*this);
    }
    
    Rational& operator/=(const Rational rat){
        this->div(rat);
        return (*this);
    }
    
    Rational& operator/=(const int rat){
        Rational r1;
        r1.numerator_ = rat;
        r1.denominator_ = 1;
        (*this) /= r1;
        return (*this);
    }
    
    Rational operator-(){
//        Rational r1;
//        r1.numerator_ = this->numerator_;
//        r1.denominator_ = this->denominator_;
        this->neg();
        return *this;
    }
    
    Rational operator+(){
        Rational r1;
        r1.numerator_ = this->numerator_;
        r1.denominator_ = this->denominator_;
        r1.neg();
        return r1;
        //this->neg();
       // return *this;
    }
    
    Rational operator+(Rational r1){
        Rational r2;
        r2.numerator_ = this->numerator_;
        r2.denominator_ = this->denominator_;
        r2.add(r1);
        return r2;
    }
    
    Rational operator-(const Rational r1){
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.sub(r1);
        return r2;
    }
    
    Rational operator*(const Rational r1){
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.mul(r1);
        return r2;
    }
    
    Rational operator/(const Rational r1){
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.div(r1);
        return r2;
    }
    
    Rational operator+(const int rat){
        Rational r1(rat, 1);
        Rational r2;
        r2.numerator_ = this->numerator_;
        r2.denominator_ = this->denominator_;
        r2.add(r1);
        return r2;
    }
    
    Rational operator-(const int rat){
        Rational r1(rat, 1);
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.sub(r1);
        return r2;
    }
    
    Rational operator*(const int rat){
        Rational r1(rat, 1);
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.mul(r1);
        return r2;
    }
    
    Rational operator/(const int rat){
        Rational r1(rat, 1);
        Rational r2;
        r2.numerator_ = (*this).numerator_;
        r2.denominator_ = (*this).denominator_;
        r2.div(r1);
        return r2;
    }
    

private:
    int numerator_;
    unsigned denominator_;
};

Rational operator+(const int a, const Rational r1){
        Rational r2(a, 1);
        r2.add(r1);
        return r2;
    }

Rational operator-(const int a, const Rational r1){
        Rational r2(a, 1);
        r2.sub(r1);
        return r2;
    }

Rational operator*(const int a, const Rational r1){
        Rational r2(a, 1);
        //r2.mul(r1);
        return r2;
    }

Rational operator/(const int a, const Rational r1){
        Rational r2(a, 1);
        //r2.div(r1);
        return r2;
    }

int main(){
    
    Rational r1(6,1);
    Rational r2(7,1);
    int a = 1;
    int b = 2;
    

    r1 =r1 + r2;
    cout<<r1.to_double()<<endl;

//    -r1;
//    cout<<r1.to_double()<<endl;
//    r1 =-r1;
//    cout<<r1.to_double()<<endl;
//    -r1;
//    cout<<r1.to_double()<<endl;
//    r1 =-r1;
//    cout<<r1.to_double()<<endl;
//    int a = 1;
//    cout<<a<<endl;
//    -a;
//    cout<<a<<endl;
//    a=-a;
//    cout<<a<<endl;
//    -a;
//    cout<<a<<endl;
//    a=-a;
//    cout<<a<<endl;
    
    return 0;
}