Description
Problem:
Your friend the biology lab assistant has a new job and now needs to monitor different
populations of rabbits used in his lab. He needs to be able to predict the size of the
population based on the initial population size and the average birth and death rates of
the rabbits.
Write a program that asks the user for an initial population size, the birth rate and
death rate, and the number of years to monitor the population. Then calculate and
output a table of changes in population size over those years.
The formula to compute the new population is:
N = P + B * P – D * P
where N is the new population size, P is the previous population size, B is the birth rate,
and D is the death rate. The birth and death rates are between 0 and 1.
Your program should output a table showing the starting population and the new
population at the end of each year that the population is being monitored. To output
the table, you will calculate the first year population using the initial population size for
P, then calculate the second year using the first year population for P and so on, until
you have calculated all of the requested years.
Finally, if the growth rate (birth rate – death rate) is positive you will notify the user in
which year the population will double in size. The formula to calculate this is:
n = log(2)/ log(1 + r)
where log is a function in the cmath library, and r is the growth rate. If the growth
rate is negative, you should notify the user in which year the population will become 0.
The formula to calculate this is:
n = log(1/P)/ log(1 + r)
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where P is the initial population size and r is the growth rate. If the growth rate is 0,
you should notify the user that the population is stable.
After calculating these values, ask the user if they want to run the calculator again, and
repeat as requested (accept ‘y’ or ‘Y’ as yes).
Input:
Ask the user for the initial population size, the birth rate, the death rate, and the
number of years of population changes to report. The birth rate and death rate may
have fractional values. You should validate the input as follows:
• The initial population size should be at least 100 but not more than 1,000,000.
• The birth rate and death rate should be greater than 0 and less than or equal to 100.
• The years should be greater than 0.
If the input is out of range, use an informative prompt to ask the user to re-enter valid
data until the input is valid.
For the calculations to work properly, you must convert the birth and death rates which
are input as a percent (i.e. 3.5%) to fractional values between 0 and 1 (i.e. 0.035).
Processing: You must use the following 5 functions in your program.
getInput: has four reference parameters to input initial population size, birth rate, death
rate, and number of years from the user.
calculatePop: has 3 parameters: population size, birth rate, and death rate. Returns the
calculated new population size. Do not do any output from this function.
yearsToDouble: has 1 parameter, the growth rate (which should be positive). Returns
the calculated number of years it takes for the population to double in size. Do not do
any output from this function.
yearsToZero: has 2 parameter, the initial population and the growth rate (which should
be negative). Returns the calculated number of years it takes for the population to
reach 0. Do not do any output from this function.
outputTable: has 4 parameters: initial population size, birth rate, death rate, and total
years. It outputs the table with column headers, and one row for each year from 0 to
total years, showing the population size at the end of that year.
Output: Display the years and population size as whole numbers. Use the function
floor in the cmath library to output the population sizes as whole numbers. The
values in the table should line up (right-justified). You may assume that the population
size will fit within 20 characters. Use the function ceil in the cmath library to output
the number of years to double and to reach 0 as whole numbers.
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Sample output:
Enter the initial population: 500
Enter the annual birth rate (as % of current population): 15
Enter the annual death rate (as % of current population): 10
Enter the number of years of population changes: 20
Year Population
—- ——————
0 500
1 525
2 551
3 578
4 607
5 638
6 670
7 703
8 738
9 775
10 814
11 855
12 897
13 942
14 989
15 1039
16 1091
17 1146
18 1203
19 1263
20 1326
Population will double in 15 years.
Would you like to run the calculator again(Y/N)?: y
Enter the initial population: 100
Enter the annual birth rate (as % of current population): 1
Enter the annual death rate (as % of current population): 45
Enter the number of years of population changes: 10
Year Population
—- ——————
0 100
1 56
2 31
3 17
4 9
5 5
6 3
7 1
8 0
9 0
10 0
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Population will be zero in 8 years.
Would you like to run the calculator again(Y/N)?: n
Additional Requirements:
• Your program must compile and run, otherwise you will receive a score of 0.
• Your program must pass Test Case 0 (below) or you will receive a score of 50 or
less with no credit for the other grading categories (correctness/constraints/style):
Input: population size = 500, birth rate = 15, death rate = 10, years = 20.
Expected output: see the first table in the sample output above. Years to double
and option to run the calculator again are not required to pass Test Case 0
(they ARE required for a complete solution to the assignment). Your code must
implement the two functions calculatePop and outputTable to pass Test Case 0.
• You may use integer or floating point data type to store the initial population size.
• Your program MUST define and call the functions described above.
Style:
See the Style Guidelines document on the course website. Especially pay attention
to the comments required for functions. The grader will deduct points if your
program violates the style guidelines.
Logistics:
Name your file assign6_xxxxx.cpp where xxxxx is your TX State NetID (your
txstate.edu email id). The file name should look something like this: assign6_js236.cpp
There are two steps to the turn-in process:
1. Submit an electronic copy using the Assignments tool on the TRACS website for
this class (tracs.txstate.edu). Submit the .cpp file, (NOT a .cbp file!).
2. Submit a printout of the source file at the beginning of class on the day the
assignment is due. Please print your name on the front page, and staple if there
is more than one page.
See the assignment turn-in policy on the course website (cs.txstate.edu/~js236/cs1428)
for more details.
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