[] and * operator overloading for a Rational class in c++ - overloading

Question

I'm having difficulty trying to overload the [] and * operators. This is the given code:
#include<iostream>
class Rational {
public:
Rational (int numerator=0, int denominator = 1) : n(numerator), d(denominator) { }
private:
int n, d;
};
std::ostream& operator<<(std :: ostream& out, const Rational& r) {
return out << r[0] << '/' << r[1] << std::endl;
}
int main() {
Rational rat1(2,3), rat2(3,4);
std::cout << rat1 << std::endl;
std::cout << rat1 * rat2 << std::endl;
}
Please overload [] and * operator for class Rational
I tried the following:
#include<iostream>
class Rational {
public:
Rational (int numerator=0 , int denominator = 1) :
n(numerator),d(denominator)
{ }
int operator[](int i){
if(i==0)
return n;
else return d;
}
Rational& operator*(Rational& rhs){
return *this(n*(rhs.n),d*(rhs.d));
}
private:
int n,d;
};
std::ostream& operator<<(std :: ostream& out , const Rational& r) {
return out<<r[0]<<'/'<<r[1]<<std::endl;
}
int main(){
Rational rat1(2,3) , rat2(3,4);
std::cout<<rat1<<std::endl;
std::cout<<rat1*rat2<<std::endl;
}
After trying this I get the following errors:
error: passing ‘const Rational’ as ‘this’ argument of ‘int Rational::operator[](int)’ discards qualifiers [-fpermissive]
return out<<r[0]<<'/'<<r[1]<<std::endl;
error: passing ‘const Rational’ as ‘this’ argument of ‘int Rational::operator[](int)’ discards qualifiers [-fpermissive]
return out<<r[0]<<'/'<<r[1]<<std::endl;
What am I doing wrong?

Answer 1

The problem is this line:
return *this(n * (rhs.n), d * (rhs.d));
It should be
return * new Rational(n * rhs.n, d * rhs.d);
You need to create and return a new Rational by calling the constructor, which is never done via the this pointer.
You should also validate the input: rat1[6] should generate an error.