CS 14 - Lab 7

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Virtual Functions

You will be using the code you wrote from last weeks lab and adding to it to demonstrate the use of virtual functions.

An Abstract Base Class is a class in which you never intend to declare an object of that type. It is solely used with inheritance to provide an appropriate base class from which classes may inherit interface or implementation. Abstract Base Classes typically do not contain data members. This is an example of an Abstract Base Class.

Shape.h has a couple of virtual functions. The first two are called getArea and getVolume and simply return zero. These functions will be used in the following way. The point class will inherit the Shape class, thus inheriting these functions. This is appropriate since the area and volume of a point are both zero. However, Circle inherits Point and provides its own getArea function which will overide the zero returning getArea function. However, the volume of a Circle is still zero. Cylinder inherits from Circle and redefines its own getArea and getVolume functions.

The virtual function printShapeInfo does not do anything in the Shape function and each function will overide this function to print the type of shape it is.

Pre-lab Preperation

You must complete lab 6 before this lab section. You will use your code from lab 6 to build upon.

The Lab

  • Add the shape class to your code from lab 6. Make Point inherit the Shape class
  • Add a virtual function called printShapeInfo to the classes Point, Circle, and Cylinder that prints the type of object to the screen and the information stating the location of the object (note, do not include the printing of the area or volume in this function). You may use your overloaded insertion operator if you'd like. To do this you would have to dereference the this pointer.
  • Write a member function getArea in the class Cylinder that computes and returns the surface area of a cylinder. The formula is: 2 * circleArea + 2 * PI * radius * height
  • Check your code and verify for yourself how the virtual functions are working. You may use main.cc for testing your code. The output of this code should look something like this.

    Point Breakdown - In Lab Demo

    For this assignment, you will demo your program in lab. Please show the output from main.cc to the TA. Remember, you can get partial credit for showing that you have some of the correct results. The TA will also look at your code for correctness when checking out. Remember, to receive credit for this lab, you MUST turn the code in online as well as demo in lab, however, you will only receive points for what you demo to the TA during lab section. If you do not turn in your code online, you will lose points for your lab. All code must be turned in online for archival purposes. Remember to put both partners names on the code that you turn in.

    Remeber to compile your code using the flags "-g -Wall -W -Werror -pedantic". You must use a makefile.