The objective of this assignment is to give you some practice using inheritance, virtual functions, and polymorphism. With a focus on dynamic binding, this program shifts the focus from design time static binding of functions to objects to run-time (or dynamic binding). It leverages the use of virtual functions and introduces the concept of abstract and concrete classes in its implementation of pure virtual functions as it also demonstrates polymorphic behavior.
1. Create a base class called Insect. All insects belong to an Order [i.e. "Hemiptera" (ants), Siphonaptera (fleas), Termitoidae (termites), Gryllidae (crickets), etc.] and have a size that is measured in millimeters (use a double data type). Provide a default constructor that initializes the size to zero and outputs the message Invoking the default Insect constructor and another constructor that allows the Order and size to be set by the client. This other constructor should also output the message Invoking the 2-argument Insect constructor. Also create a destructor for this class that outputs the message Invoking the default Insect destructor. Your Insect class should have a function called Eat that cannot be implemented. That is, it should be declared as a purely virtual function. Your class should also have Get and Set methods to allow the order and size to be accessed.
2. From the Insect class, derive Ant, Locust, Butterfly, and Termite classes. The derived classes should each have constructors and destructors that output an appropriate message (e.g., the Ant constructor outputs "Invoking Ant constructor," and the Ant destructor outputs Invoking Ant destructor). The constructor of each derived class should allow the Order and size of the Insect to be set (think member initialization list). The derived classes should each have a member function called Eat that overrides the Insect Eat version. Ant Eat should output As an ant, I eat everything, Locust Eat should output As a locust, I eat leaves, Butterfly Eat should output As a butterfly, I eat nectar, and Termite Eat should output As a termite, I eat wood.
3. Write a main function that uses the Insect and derived classes as needed to do the following. You must perform the actions below in the sequence described (i.e., do not take a shortcut around using dynamic memory allocation/deallocation and virtual methods since they are the whole point of the lab).
a. Use the rand() function in a formula to generate a random size in millimeters based on the insect selected. The range of sizes for each insect are as follows:
Ant: .01 to 1.0 millimeters
Locust: 10.5 to 50.0 millimeters
Butterfly: 40.0 to 75.5 millimeters
Termite: 1.5 to 5.5 millimeters
As a refresher on the rand() function, recall that it generates an integer between 0 and the largest integer that can be stored. If you don't want the low end of the range to start at 0, you add a number to the rand() function that represents the smallest number in the range of numbers you want to generate. This is the offset. Using the modulus operator (%), you can specify the interval. For example, to generate a random number between 2.75 and 4.00, you can use this formula (note that since rand() generates an integer, I am multiplying the desired offset and interval by 100 and then dividing the final result by 100.0):
double randomNumber = ((rand() % interval ) + (offset))/100.0
randomNumber = ((rand() % (125+1)) + (275))/100.0
where 125 = 400-275
"1" is added to the 125 to make the range inclusive on the upper end.
Although not for this assignment
An alternative to using the rand() function is to use the uniform_real_distribution class, which is described in section 13-6 of your textbook. It's actually much easier to use and more robust in terms of generating random numbers that are more random. The rand() function is somewhat predictable, but it's still used in programs today. It's always good to know both techniques, though. In this assignment, though, to receive credit for generating the random number, you must use the rand() function.
b. Your program should use a seed value of 100 for the random number generator. You should set the seed only once at the beginning of main(). Use the srand() function to set the seed.
c. Prompt the user to make an Insect selection [e.g. (1) for Ant, (2) for Locust, (3) for Butterfly, and (4) for Termite] and to enter an Order for the insect. Dynamically create an Ant, Locust, Butterfly, or Termite object (depending on what the user entered) and initialize it with a constructor to which is passed its Order and size. Save the object (use an array called "insects" - credit will not be awarded if you use a vector for this). You may hardcode the size of the array to hold 3 elements. That is, you don't need to dynamically create this array unless you want to. If you do dynamically allocate it, though, be sure to deallocate its memory properly.
d. Repeat steps a. and b. 2 more times. You do not know what insects the user will select or in what order, so you must figure out how to create and store the appropriate objects. Notice that there are 4 insects from which to choose, but the user will only make 3 selections. Therefore, one insect will not be chosen.
e. After the user has entered all 3 selections, execute another loop that cycles through the 3 selections and invokes the Eat function and also displays the Order and size of the insect. If you have done it properly, each of your outputs will correspond to the type of Insect the user selected in the order he or she entered them.
Your input screen should look something like this:
Main Menu
1 - Ant
2 - Locust
3 - Butterfly
4 - Termite
Enter selection:
As each insect is selected, you should be prompted to enter the insect's Order:
Enter selection: 3
Enter the Order associated with the insect you selected: Lepidoptera
As each insect is created, you should see messages like the following:
Invoking Insect 2-argument constructor
Invoking Butterfly 2-argument constructor
Your final output screen shout look something like this:
My Order is Lepidoptera, and I am 43.65 millimeters long.
As a butterfly, I eat nectar.
My Order is Termitoidae, and I am 1.63 millimeters long.
As a termite, I eat wood.
My Order is Caelifera, and I am 25.14 millimeters long.
As a locust, I eat leaves.
Invoking the Butterfly destructor
Invoking the Insect destructor
Invoking the Termite destructor
Invoking the Insect destructor
Invoking the Locust destructor
Invoking the Insect destructor
Press any key to continue...