CMSC 201 Fall 2006 - Project 1 - Predator/Prey Simulation

CMSC201

Programming Project One
Predator/Prey Simulation

Out: Tuesday 9/26/06

Due: Tuesday 10/3/06,
Before Midnight

The Objective

The objective of this assignment is to get you started writing programs in C in the UNIX environment. Its main emphasis is design, so we will be designing the project together in class. This project will also give you practice writing functions, loops, switch statements and using separate compilation.

The Background

Populations of predators and their prey that are isolated tend to achieve an equilibrium over time. The pattern tends to be a cyclic increase and decrease in the populations. When the number of predators is low, the number of prey grow. As the prey increase the predators manage to catch more of them. The predators are now healthier and can raise their young with fewer dying out, so the number of predators increases. Now since there are more predators, they will start to reduce the number of prey. When the number of prey decreases too far, the predators won't be able to catch enough of them and the predators will start to die of starvation. That's the cycle.

Those of you who are interested in the predator/prey relationship, might find the following website interesting. It is a National Park Service publication about the moose and wolf populations on Isle Royale .

We will be studying a fictional population of rabbits and/or foxes isolated on an island and will make the following assumptions:

Rabbits only die by being eaten by foxes
Foxes only die from natural causes
The interaction between foxes and rabbits can be described by a function.

Population Formulas

For Rabbit Populations :
If no foxes are present the new rabbit population is calculated from the previous population by the following equation:
P_Rn = P_R(n-1) + B_R * P_R(n-1)
where :
- P_Rn is the new rabbit population after time period n
- P_R(n-1) is the beginning rabbit population at the time period n-1
- B_R is the birth rate for rabbits
Under these conditions the rabbit population would continually increase.
For Fox Populations :
If no hunters are present the new fox population is calculated from the previous population by the following equation:
P_Fn = P_F(n-1) - D_F * P_F(n-1)
where:
- P_Fn is the new fox population after time period n
- P_F(n-1) is the beginning fox population at the time period n-1
- D_F is the death rate for foxes
Under these conditions the fox population will decrease.
For Both Foxes and Rabbits Coexisting :
When foxes can eat rabbits the population equations have another term to describe the interaction between the two.
The population of rabbits is the same as above with a loss of population due to foxes :
P_Rn = P_R(n-1) + B_R * P_R(n-1) - I * P_R(n-1) * P_F(n-1)
where :
The population of foxes is increased with the addition of the interaction term :
P_Fn = P_F(n-1) - D_F * P_F(n-1) + I * P_F(n-1) * P_R(n-1)
Now the population of rabbits is decreased by the foxes with the greater number of foxes causing a greater decrease in the rabbit population. This means that the rabbit population is eventually going to decrease and the resulting fox population will also decease. As a result a cyclic increase and decrease in the populations are set up. This is what is observed in the simulation.

Formulas and their descriptions courtesy of J. Barry DeRoos of messiah.edu

The Task

You are to write a program that simulates populations of rabbits, foxes or both over time, using the formulas shown above. Certainly there can never be a negative number of rabbits or foxes, so if the calculation of rabbits indicates that there should be a negative number of rabbits, change the number of rabbits to 0. We are also capping the populations at 500 individuals of each type. So if the calculations produce an answer of greater than 500 foxes, the number of foxes should be changed to 500. It is possible to have 500 rabbits and 500 foxes at the same time.

You will have to get input from the user for the following values:

The original rabbit population, numRabbits (int)
The original fox population, numFoxes (int)
The birth rate of rabbits, birthRate (float)
The death rate of foxes, deathRate (float)
The interaction constant, interaction (float)
The number of years to run the simulation, years (int)

After printing the program explanation and getting the initial values necessary for the simulation, you will display a menu that will allow the user to choose which kind of population to simulate or to change the interaction constant. The choices must be:

Simulate a Population of Rabbits Only
Simulate a Population of Foxes Only
Simulate a Population with Rabbits & Foxes Interacting
Change Interaction Constant
Quit

You will be expected to write twelve functions, other than main(), for this project.

Here are the function prototypes:

void PrintGreeting (void); int GetValidInt (int min, int max); float GetValidFloat (float min, float max); void PrintMenu (void); void SimulateRabbits (int numRabbits, int numFoxes, float birthRate, float interaction, int years); void SimulateFoxes (int numRabbits, int numFoxes, float deathRate, float interaction, int years); void SimulateBoth (int numRabbits, int numFoxes, float birthRate, float deathRate, float interaction, int years); int CalculateRabbits (int numRabbits, int numFoxes, float birthRate, float interaction); int CalculateFoxes (int numRabbits, int numFoxes, float deathRate, float interaction); float ChangeInteraction (void); void PrintHeading (int numRabbits, int numFoxes, float birthRate, float deathRate, float interaction, int years); void PrintTableLine (int time, int numRabbits, int numFoxes);

You MUST use these function prototypes, as shown, without modification.

Function Descriptions:

PrintGreeting() - should print a message to the user, explaining what the program will do.
GetValidInt() - should prompt the user for an integer within the range of min to max, inclusive, that are passed in as arguments. It assures the integer entered is within that range and returns it.
GetValidFloat() - should prompt the user for a value within the range of min to max, inclusive, that are passed in as arguments. It assures the value entered is within that range and returns it as a float.
PrintMenu() - should print the menu to the screen
SimulateRabbits() - simulates a population composed of rabbits only by printing a table showing the populations each year. The values on each line are found by calling CalculateRabbits().
SimulateFoxes() - simulates a population composed of foxes only by printing a table showing the populations each year. The values on each line are found by calling CalculateFoxes().
SimulateBoth() - simulates a population composed of both rabbits and foxes by printing a table showing both populations each year. The values on each line are found by calling CalculateRabbits() followed by calling CalculateFoxes(). Hint: You'll need to keep the previous number of rabbits to pass to CalculateFoxes().
CalculateRabbits() - returns the new number of rabbits by implementing the formula
P_Rn = P_R(n-1) + BR * P_R(n-1) - I * P_R(n-1) * P_F(n-1)
but keeping the population within the range 0 <= numRabbits <= 500.
CalculateFoxes() - returns the new number of foxes by implementing the formula
P_Fn = P_F(n-1) - DF * P_F(n-1) + I * P_F(n-1) * P_R(n-1)
but keeping the population within the range 0 <= numFoxes <= 500.
ChangeInteraction() - allows the user to change the interaction constant by calling GetValidFloat() and returning the new value to be used
PrintHeading() - takes the initial values entered by the user and prints the appropriate title, values and the column headings for the table.
PrintTableLine() - takes the current year, the current number of rabbits and the current number of foxes and prints them as one line of the table.

Sample Run

Since the output is long, here is a link to a separate webpage containing the sample run.

More Details

You MUST use the prototypes as shown without any modification.
You MUST use separate compilation. Your files must be named proj1.c, util.c and util.h, where proj1.c should contain main(), and the functions that are project specific (can't be used in other projects). The file util.c should contain the function definitions of the modules, GetValidInt() and GetValidFloat(), since they will be useful with other projects. util.h should contain the function prototypes for the functions found in util.c
You MUST use symbolic constants for all numeric values, therefor you will need the following #defines :
The design for this project is to be given in lecture on 9/26/04 and 9/27/04. Your project MUST be written as it is designed in class.

Submitting the Program

To submit the file you should use the command:

submit cs201 Proj1 proj1.c util.c util.h

You can check your submission by using the command:

submitls cs201 Proj1

Tuesday, 26-Sep-2006 08:29:21 EDT