c++ two versions of overloading subscript operator

Question

My question is about the difference between:

const T& operator[](const int nIndex) const;

and:

T& operator[](const          


        

Answer 1

If the object you're accessing is const, you don't want to be able to modify it. The compiler wouldn't let you call the non-const version of the function.

const vector mints;

mints[3] = 5; // not allowed by compiler