Programming Project: Extending the
Marine Biology Case Study
Using Inheritance

Extend the Marine Biology case study simulation to support fish, sharks, and insects, all of which eat, breed, move, and, eventually, die. Fish, sharks, and insects are all swimming animals, so you should abstract the common behavior of all three classes into a SwimmingAnimal superclass.

Processing Order:

All sharks are processed first, then the fish, and finally the insects.

Breeding:

If an animal is of breeding age, and if the time since its last meal is no more than 2 time steps, then it breeds. It does this by replacing itself with up to five children, one in the its own position and one in each of the empty neighboring positions to the North, South, East, or West. The newly created children (including the one that replaces the original animal) are all of age 0. The number of time steps since their last meal is also 0.

Eating:

If a fish or shark is not at the correct age to breed, then it attempts to eat a random neighboring animal lower in the food chain, moving to that animal's location in the process and resetting the time since the animal's last meal to 0. If there are no neighboring animals to eat, then the number of time steps since the animal's last meal is incremented.

Moving:

If an animal has not bred or moved as a result of eating, then it randomly chooses an empty neighboring position to which to move.

Aging and Dying:

After breeding, eating, or moving, an animal ages one time step. If it reaches its expected life span, or if it has not eaten within the last three time steps (fish and sharks only), then the animal dies. (In other words, it is removed from the environment.)

Species-Specific Information:

Sharks breed at age 5 and die when they reach age 7. They eat fish.

Fish breed at age 3 and die when they reach age 5. They eat insects.

Insects breed at age 1 (but not age 0!) and die when they reach age 3. They probably eat something, but whatever it is is not represented in our simulation.

Miscellaneous:

In order to recognize whether a neighbor is a potential feast, your program will need to be able to ask any animal what its type is. This is not as easy to do in C++ as we might like, so you should provide a function in the superclass that returns a string that indicates the type. Each subclass will obviously have to redefine the function to return the proper string. You can use this function in client code without hard-coding what the string is, as in the following example.

      // Assume that "animal" is a pointer to some kind of animal.
      Fish f;
      if ( animal->Type() == f.Type() )
	  // lunch!
  

Whatever the string is that Type returns, animal's type will only match f's type if animal is a fish.

Remember that the objects you are dealing with are clones. Therefore, it is important that you update the environment after the animal has done everything for the time step (including aging). Any changes made to the clone object after a call to Update will not be reflected in the environment.