const overloaded operator[] function and its invocation

Question

I define two versions of overloaded operator[] function in a class array. ptr is a pointer to first element of the array

Answer 1

Your const version should return const int& not int, so that the semantics are just the same between the two functions.

Once you've done that, it doesn't matter which one is used. If the const version has to be used because your object has a const context, then it will be... and it won't matter as you're not trying to modify anything. Otherwise, it'll use the non-const version... but with just the same effect.