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Classes
Private and public
  class Zoo {
    // private as default ...
  public:
    // what follows is public until ...
  private:
    // ... here, where we switch back to private ...
  public:
    // ... and back to public.
  };
 class Struct {
  public:       // Structure elements are public by default
    // elements, methods
  };
This declares a class Point and defines an object apoint. You can think of a class definition as a structure definition with functions (or ``methods''). Additionally, you
can specify the access rights in more detail. For example, _x and _y are private, because elements of classes are private as default. Consequently, we explicitly
must ``switch'' the access rights to declare the following to be public. We do that by using the keyword public followed by a colon: Every element following this
keyword are now accessible from outside of the class.
Recall that a structure struct is a combination of various data elements which are accessible from the outside. We are now able to express a structure with help of
a class, where all elements are declared to be public.
This is exactly what C++ does with struct. Structures are handled like classes. Whereas elements of classes (defined with class) are private by default, elements
of structures (defined with struct) are public. However, we can also use private: to switch to a private section in structures.