C ++ operator overload ++

Question

which one of the two codes is right and why ?

C C::operator++() {
    x++; 
    y++; 
    return *this; 
}


C & C::operator++() {
    x++; 
    y++; 
    return *this; 
}

Thanks

Answer 1

The second one is the idiomatic one: a parameter-less operator++ is the pre-fix increment operator, which should return a reference to self.

Answer 2

Both are "correct", but the second is idiomatic, because it's expected that the prefix operator ++ returns an lvalue.