CMPS 223 - Homework 1

Homework 1 - Inheritance and Polymorphism

Due: Wednesday April 7, 2010 at 5:00pm

Coding Conventions

The following coding conventions should be used for all assignments.

Have a comment section at the top of your files with your name, the assignment number and the date the code was written. You may add more to the top comment if you wish.
Put a blank line between each function body (including between main and user defined functions), between the header section (#include and using namespace) and the function prototype section, and between the function prototypes and the main function.
Indent all blocks such as if statements or loops with at least two spaces. For example, your if statements should appear as:
```
if(a == b)
{
  a = a * 2;
  b = b - 1;
}
```
NOT as:
```
if(a == b)
{
a = a * 2;
b = b - 1;
}
```
If you use vim on Sleipnir, it will indent such blocks automatically for you.

Assignment

The purpose of this assignment is to create a class hierarchy using inheritance and to see how polymorphism works when using a pointer of a parent class. You will be defining three classes with the following hierarchy:

                       Shape
                      /     \
                     /       \
                   Line    Circle

Shape class

The Shape class is the parent class for this exercise. It defines the general characteristics of the shapes: a set of (x,y) coordinates and a length. The Shape class should have the following:

Protected member variables

Integers for x, y and length

Public member functions

A default constructor that sets all variables to the value 0
A copy constructor
A constructor that takes three integers to set the three variables
virtual void print_shape() - A polymorphic function that prints "Undefined shape" to stdout for the Shape class and will be redefined in the children classes.
void set_shape(int, int, int) - A function that takes three integers to set the values of x, y and length.

Line class

This is a child class of the Shape class. For simplicity, this class will be just a straight line. The (x,y) coordinate is the start of the line and length indicates how long the line is.
(Note: You could implement slope by having a new member variable for this class)

Public member functions

Default constructor (can invoke parent constructor)
Copy constructor (can invoke parent constructor)
Constructor that takes three integers (can invoke parent constructor)
virtual void print_shape() - For this class, print_shape should print "Shape: Line X value: <x> Y value: <y> Length: <length>" to stdout.

Circle class

This is a child class of the Shape class. The (x,y) coordinate is the center of the circle and length is the radius.

Member functions

Default constructor (can invoke parent constructor)
Copy constructor (can invoke parent constructor)
Constructor that takes three integers (can invoke parent constructor)
virtual void print_shape() - For this class, print_shape should print "Shape: Circle Center: (<x>, <y>) Radius: <length>" to stdout.

Menu Program

The menu program allows you to test if your implementation of the above classes are correct. Your menu should be implemented in a fashion similar to menu_example.cpp.

Your main() function MUST have a pointer variable of type Shape that will be used to store the current shape. Remember to delete the current shape before allocating a new one. You will then call the set_shape() and print_shape() member functions using this parent class pointer. See pointer_example.cpp for an example of this.

Your menu should be as follows:

   Welcome to the Shape Menu
  ===========================
  1.  Create a new line
  2.  Create a new circle
  3.  Print the current shape

  0.  Exit
  ===========================

Options 1 and 2 should try to allocate a new line or circle object, check that the new line/circle was actually allocated and print a message if the allocation failed. Be SURE to deallocate any old shape before allocating a new shape when Option 1 or 2 is selected.

If the allocation works, Option 1 should prompt the user for the x,y coordinates of the origin of the line and the length of the line. It should then read those values into temporary integers. It should then call set_shape() to pass the values into the Line object.

Likewise, if allocation works, Option 2 should prompt for the x,y coordinates of the origin of the circle and the radius of the circle, read those values into temporary integers and call set_shape() to pass those values into the Circle object.

Option 3 should gracefully handle the case where 3 is selected before 1 or 2 (i.e. when there is no shape object allocated). It should print an error message about no shape existing (core dumps when 3 is selected first will be a deduction in your grade). If there is a shape allocated, Option 3 should call print_shape() to print information about the shape.

Submit your completed code as an attachment in an email to the instructor. If you use multiple files (seperate compilation), be sure to include all files in the attachment list.