Operator Overloading - General Questions

What will be the output of the program?

#include <iostream>
using namespace std;
struct F {
    int k;
    int operator()(int x) const { return k * x; }
};
int main() {
    F triple{3};
    cout << triple(7) << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
struct C {
    int n;
    C &operator+=(int k) { n += k; return *this; }
};
int main() {
    C c{1};
    (c += 2) += 3;
    cout << c.n << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
struct V {
    int x, y;
};
ostream &operator<<(ostream &os, const V &v) { return os << "(" << v.x << "," << v.y << ")"; }
int main() {
    V v{2, 5};
    cout << v << endl;
    return 0;
}

Which operator must be overloaded as a member function?

Operator overloading can change an operator's: