calculate monthly payment

This is a discussion on calculate monthly payment within the C Programming forums, part of the General Programming Boards category; Hey guys, new to the board and C programming in general. I have this assignment that's giving me problems, don't ...

  1. #1
    Registered User
    Join Date
    Oct 2010
    Posts
    63

    Question calculate monthly payment

    Hey guys, new to the board and C programming in general. I have this assignment that's giving me problems, don't know what's wrong.


    Monthly Pay=[ rate + rate /([1+rate]^months -1)] X principle
    Where rate of %6 means 6/1200
    Months means number of years x 12

    "Possible data to test:
    Principle 12200
    Rate 7%
    Term in years 5
    Monthly payment is: 241.57"

    My code:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    
    void main ()
    {
        double princ, rate, term, monthly;
            
        printf("Please enter the the principle on your payment: ");
        scanf("%lf", &princ);
        printf("Please enter the rate on your payment: ");
        scanf("%lf", &rate);
        printf("Please enter the term of your payment in years: ");
        scanf("%lf", &term);
        
        rate = (rate/1200);
        term = (term*12);
        
        monthly = ((rate + (rate/(pow((1 + rate),(term-1))))) * princ);
            
        printf("Your monthly payment is: %f", monthly);
        
        return 0;
    
    }
    For my monthly payment I always end up getting half of what is expected. Any ideas?

  2. #2
    Registered User Swarvy's Avatar
    Join Date
    Apr 2008
    Location
    United Kingdom
    Posts
    195
    The problem is the formula you are using. You are doing the following on the denominator.
    Code:
    pow(1+rate, term-1)
    What you should be doing is this:
    Code:
    pow(1+rate, term) - 1
    Btw, it is very bad programming technique to use 'void main()'. You should be using 'int main()' instead.

  3. #3
    Registered User
    Join Date
    Oct 2010
    Posts
    63
    Thanks Swarvy! Just compiled it, changed the void as well, and it runs fine.

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