C ++ ++ operator overload

Question

which 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 is idiomatic: the-less option operator++is a pre-fix increment operator that should return a reference to self.

Answer 2

Both are "correct", but the second is idiomatic because he expected the prefix to operator ++return an lvalue.