Wrap-Up

Answers to Self Review Exercises

13.1	a) derived-class object. b) switch. c) abstract. d) concrete. e) dynamic_cast. f) type_info. g) Polymorphism. h) virtual. i) downcasting.
13.2	a) False. An abstract base class can include virtual functions with implementations. b) False. Referring to a base-class object with a derived-class handle is dangerous. c) False. Classes are never declared virtual. Rather, a class is made abstract by including at least one pure virtual function in the class. d) True. e) True.

Exercises

13.3	How is it that polymorphism enables you to program "in the general" rather than "in the specific"? Discuss the key advantages of programming "in the general."
13.4	Discuss the problems of programming with switch logic. Explain why polymorphism can be an effective alternative to using switch logic.
13.5	Distinguish between inheriting interface and inheriting implementation. How do inheritance hierarchies designed for inheriting interface differ from those designed for inheriting implementation?
13.6	What are virtual functions? Describe a circumstance in which virtual functions would be appropriate.
13.7	Distinguish between static binding and dynamic binding. Explain the use of virtual functions and the vtable in dynamic binding.
13.8	Distinguish between virtual functions and pure virtual functions.
13.9	Suggest one or more levels of abstract base classes for the Shape hierarchy discussed in this chapter and shown in Fig. 12.3. (The first level is Shape, and the second level consists of the classes TwoDimensionalShape and THReeDimensionalShape.)
13.10	How does polymorphism promote extensibility?
13.11	You have been asked to develop a flight simulator that will have elaborate graphical outputs. Explain why polymorphic programming would be especially effective for a problem of this nature.
13.12	(Payroll System Modification) Modify the payroll system of Figs. 13.1313.23 to include private data member birthDate in class Employee. Use class Date from Figs. 11.1211.13 to represent an employee's birthday. Assume that payroll is processed once per month. Create a vector of Employee references to store the various employee objects. In a loop, calculate the payroll for each Employee (polymorphically), and add a $100.00 bonus to the person's payroll amount if the current month is the month in which the Employee's birthday occurs.
13.13	(Shape Hierarchy) Implement the Shape hierarchy designed in Exercise 12.7 (which is based on the hierarchy in Fig. 12.3). Each TwoDimensionalShape should contain function getArea to calculate the area of the two-dimensional shape. Each ThreeDimensionalShape should have member functions getArea and getVolume to calculate the surface area and volume of the three-dimensional shape, respectively. Create a program that uses a vector of Shape pointers to objects of each concrete class in the hierarchy. The program should print the object to which each vector element points. Also, in the loop that processes all the shapes in the vector, determine whether each shape is a TwoDimensionalShape or a ThreeDimensionalShape. If a shape is a TwoDimensionalShape, display its area. If a shape is a ThreeDimensionalShape, display its area and volume.
13.14	(Polymorphic Screen Manager Using Shape Hierarchy) Develop a basic graphics package. Use the Shape hierarchy implemented in Exercise 13.13. Limit yourself to two-dimensional shapes such as squares, rectangles, triangles and circles. Interact with the user. Let the user specify the position, size, shape and fill characters to be used in drawing each shape. The user can specify more than one of the same shape. As you create each shape, place a Shape * pointer to each new Shape object into an array. Each Shape class should now have its own draw member function. Write a polymorphic screen manager that walks through the array, sending draw messages to each object in the array to form a screen image. Redraw the screen image each time the user specifies an additional shape.
13.15	(Package Inheritance Hierarchy) Use the Package inheritance hierarchy created in Exercise 12.9 to create a program that displays the address information and calculates the shipping costs for several Packages. The program should contain a vector of Package pointers to objects of classes TwoDayPackage and OvernightPackage. Loop through the vector to process the Packages polymorphically. For each Package, invoke get functions to obtain the address information of the sender and the recipient, then print the two addresses as they would appear on mailing labels. Also, call each Package's calculateCost member function and print the result. Keep track of the total shipping cost for all Packages in the vector, and display this total when the loop terminates.
13.16	(Polymorphic Banking Program Using Account Hierarchy) Develop a polymorphic banking program using the Account hierarchy created in Exercise 12.10. Create a vector of Account pointers to SavingsAccount and CheckingAccount objects. For each Account in the vector, allow the user to specify an amount of money to withdraw from the Account using member function debit and an amount of money to deposit into the Account using member function credit. As you process each Account, determine its type. If an Account is a SavingsAccount, calculate the amount of interest owed to the Account using member function calculateInterest, then add the interest to the account balance using member function credit. After processing an Account, print the updated account balance obtained by invoking base class member function getBalance.