The problem with the code above is that the cartesian_vector class accesses private members of the point class. Since we have written both classes, we are happy to bend the rules, and so we make the cartesian_vector class a friend of the point class:
class cartesian_vector; // forward decalartion class point { double x; double y; public: point(double x, double y) : x(x), y(y){} friend class cartesian_point; };
Since the cartesian_vector class is declared after the point class, we have to provide a forward declaration that essentially tells the compiler that the name cartesian_vector is about to be used and it will be declared elsewhere. The important line starts with friend. This indicates that the code for the entire ...
