CMSC104, Spring 2002
Programming Project 4
Monthly Car Payment Calculator
Out: Tuesday, March 19, 2002
Due: Thursday, April 4, 2002 before midnight
<![CDATA[
]]>
The Objective
This project is designed to give you practice writing a C program on
your own. It will give you
practice with while loops, as well as experience
working with functions from the math library.
The Background
It is time for me to purchase a new car and I need your help. I have
finally decided on the car, the Lexus SC430, but
I am not sure exactly how much the monthly
payments will be. Before I can purchase the car, I need to know if I can
afford the monthly payments on the car.
The Task
Your job is to write a program that will calculate a monthly
car payment, given the necessary input. See below for an explanation of
input. Here is the formula used to calculate the monthly payment:
<![CDATA[
monthly payment = P ( r / 12 )
-------------------------
-m
(1 - ( 1 + r / 12 ) )
where P = the principal amount,
r = the interest rate (in decimal form) and
m = the number of months
]]>
Your program should accept the following input from the user:
- The price of the car
- The sales tax (in percent format)
- The number of monthly payments
- The interest rate (in percent format)
- The amount of down payment
- The value of trade-in
- The rebate amount
Based on the user input, you are to calculate the amount of
principal. The principal is considered to be the original amount
of debt on which interest is calculated. Therefore, you must adjust
the price of the car to reflect any additions (such as sales tax) or
deductions (such as down payment). You should then calculate the monthly
payment, using the above formula. Note that in the formula, the interest
rate is in
decimal format. The interest (as well as sales tax) should be read in
from the user in percent format. For example: 7.5% would be
7.5 in percent format and .075 in decimal format.
Your program should allow the user to keep calculating
monthly payments until he or she wishes to quit. The user should
select a 1 to calculate another payment or a 0 to quit.
Assumptions
- The price of the car and the number of monthly payments
will always be greater than 0.
- Both the sales tax and interest rate will be entered in
percent format. You must convert this number to
decimal format before using it in any calculations. You can
assume the number will be between 0 and 100 inclusive.
- A value of zero is acceptable for the down payment, trade-in and
rebate
Sample Output
<![CDATA[
linux2[47]% a.out
$$$$$$ Monthly Car Payment Calculator $$$$$$
Enter the price of the car: 15000
Enter the sales tax (%): 5.0
Enter the number of months: 48
Enter the interest rate (%): 7.5
Enter the amount of the down payment: 5000
Enter the value of trade-in: 1200
Enter rebate amount: 1000
The monthly payment is: $206.73
Would you like to calculate another payment?
Please enter 1 for yes or 0 to quit: 1
Enter the price of the car: 15000
Enter the sales tax (%): 5.0
Enter the number of months: 36
Enter the interest rate (%): 6.0
Enter the amount of the down payment: 0
Enter the value of trade-in: 0
Enter rebate amount: 0
The monthly payment is: $479.15
Would you like to calculate another payment?
Please enter 1 for yes or 0 to quit: 1
Enter the price of the car: 15000
Enter the sales tax (%): 5.0
Enter the number of months: 48
Enter the interest rate (%): 0
Enter the amount of the down payment: 5000
Enter the value of trade-in: 0
Enter rebate amount: 0
The monthly payment is: $223.96
Would you like to calculate another payment?
Please enter 1 for yes or 0 to quit: 0
Thank you for using the monthly car payment calculator!
linux2[48]%
]]>
Important Note : You must tell the compiler where to find the math
library, or else your program will not work. This is accomplished by
using the -lm (the lowercase letter 'l' not the number one) option when
compiling. So in order to compile a program that
calls a function in the math library, not only do you have to #include
the math.h header file, but also must compile with the -lm option. For a
source file called proj4.c, that command would be :
<![CDATA[
linux2[269]% gcc -ansi -Wall proj4.c -lm
]]>
Submitting the Program
Here is a sample submission command. Note that the project name starts with uppercase 'P'.
submit cs104_0101 Proj4 proj4.c
To verify that your project was submitted, you can execute the
following command at the Unix prompt. It will show the file that
you submitted in a format similar to the Unix 'ls' command.
submitls cs104_0101 Proj4