CSC 172
Homework 4

Assigned March 11, due April 3, to be done solo or in teams of two

• PSP recording: As usual. Here are the PSP forms.
• The Programming Part: This is a modification of your "bookstore" program from homework 3. You are to enhance that program in two ways:
  • Modify the Item class so that, instead of having a "kind" instance variable, it has several subclasses for different kinds of items: a Textbook subclass, a Notebook subclass, etc. Item itself will become an "abstract class", i.e. a class that you can't create instances of, because it doesn't make sense to have an Item that isn't any particular kind of Item.
    • Each of these subclasses should have appropriate instance variables: for example, the Notebook class might have two instance variables pages and sections, to distinguish between a 100-page 2-subject notebook and a 200-page 5-subject notebook. However, it doesn't make sense for the Sweatshirt class to have a pages instance variable.
    • Each of these subclasses should have a constructor that initializes its instance variables appropriately. Your testItems() function should call these various constructors to create various kinds of items.
    • Each of these subclasses should have a description() or toString() method (pick a name, whichever you prefer) that returns a string describing all the relevant information about the item (including, for example, what kind of item it is and the values of all of its instance variables). In addition, the Item class should have an abstract virtual description() method. Your testItems method should store several different kinds of items in Item * variables, and print the results of their description() methods so you can see easily whether they're correct.
  • Modify the Inventory class to be a little more realistic:
    • Write a description() method that returns a string describing all the items in the inventory in an informative and useful format. (Hint: use the description() method you've already written for the Item classes.)
    • Write an add method that takes an Item * parameter and adds it to the array. This will require building a new array, one element larger than the old one, copying the contents of the old array (together with the additional item) into the new one, deleting the old one, renaming so future references to "the array" refer to the new one, and updating the size. This isn't the most efficient way to do it, but it's reasonably simple; we'll learn more efficient ways later in the semester.
    • Write a remove method that takes in the index of an element in the array of Item pointers, and removes that element from the array (if it exists; if not, your remove method should do nothing at all.) One way to do this is to create a new array one element smaller, copy all but the element to be removed into the new array, delete the old array, rename, and update the size. Another way is to just move things around within the old array and update the size; this leaves some memory allocated and unused, but it's faster.
    • Add to your testInventory function several test cases to make sure description, add, and remove all work correctly.
  • Extra credit: The description() method is really a Java-style way of doing things. It allows you to write
    Item *myNotebook = new Notebook(100, 2, 5.00); // a $5.00, 100-page, 2-subject notebook
...
cout << "My notebook is " << myNotebook->description();
    A real C++ programmer would instead write a function overriding the built-in << operator, so one could write
    Item *myNotebook = new Notebook(100, 2, 5.00); // a $5.00, 100-page, 2-subject notebook
...
cout << "My notebook is " << *myNotebook;
    Read pages 612-613 (and perhaps pages 261-300) of the Stroustrup book and write << operators for both the Item class (and all of its subclasses) and the Inventory class. Test them by putting statements like the above into the testItems and testInventory functions. You can also use my March 11 inheritance examples as a model.
• How to turn this in: The PSP forms are sent to me automatically when you use the on-line forms, so don't worry about them. Put the whole program into one folder, zip the folder, and attach the resulting zip file to your e-mail.