c++_primer_exercise_1501

Exercise 15.1:

Member function that defines type-specific behavior. Calls to a virtual made through a reference or pointer are resolved at run time, based on the type of the object to which the reference or pointer is bound.

Exercise 15.2:

public access specifier -- Members defined after a public access specifier; accessible to any user of the class. Ordinarily, only the functions that define the interface to the class should be defined in the public section.

private access specifier -- Members defined after a private access specifier; accessible only to the friends and other class members. Data members and utility functions used by the class that are not part of the type's interface are usually declared private.

protected access specifier -- Members defined after the protected keyword may be accessed by the members and friends of a derived class. However, these members are only accessible through derived objects.  protected members are not accessible to ordinary users of the class. 

Exercise 15.3: