'Private' is discussed in the previous section, and 'public' means 'anyone can access it'. The third option, 'protected', makes a member (either data member or member fn) accessible to subclasses.
Thus members defined in the 'private:' section of class X are accessible only to the member functions and friends of class X; members defined in the 'public:' section are accessible by everyone; 'protected:' members are accessible by members fns and friends of class X, as well as member fns of subclasses of X.
