calculating mortgage!!!

This is a discussion on calculating mortgage!!! within the C Programming forums, part of the General Programming Boards category; I am having troubles in my program for the mortgage calculations. the program works fine, but I keep in getting ...

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    calculating mortgage!!!

    I am having troubles in my program for the mortgage calculations. the program works fine, but I keep in getting weird numbers:
    Here is my program, if you have enough time, can you check for me, and provide me with some feedback, Thanks
    --------------------------------------------------------------------------
    insert
    Code:
    #include <stdio.h>
    #include <math.h>
    double price(double sf,double down)
    {
            double cost;
            cost=sf*18-(down/sf);
            return(cost);
    }
    double annual_fuel(double sf)
    {
            double fuel_cost;
            fuel_cost=sf*0.85/12;
            return(fuel_cost);
    }
    double mortgage(double i,double p,double n)
    {
            return(i*p/(1-pow((1+i),-1*n)));
    }
    int main(){
    double down_pay,sq_foot,mon_interest_rate,num_pay,principle;
    printf("\nPlease, Enter the sq. Footage:  ");
    scanf("%lf",&sq_foot);
    printf("\nNow, Enter the Down Payment: ");
    scanf("%lf",&down_pay);
    printf("\nPlease, Enter the monthly interest rate in percentage: ");
    scanf("%lf",&mon_interest_rate);
    mon_interest_rate=mon_interest_rate/(12*100); // convert from annual to
    monthly rate
    printf("\nplease, Enter the annual number of payments:  ");
    scanf("%lf",&num_pay);
    principle=price(sq_foot,down_pay)-down_pay+annual_fuel(sq_foot);
    printf("\n      Your house cost is $%0.2lf",price(sq_foot,down_pay));
    printf("\n      Your cost after fuel cost is
    $%0.2lf",annual_fuel(sq_foot)+price(sq_foot,down_pay));
    printf("\n      Your monthly payment is $%0.2lf\n
    ",mortgage(mon_interest_rate,principle,num_pay));
    return 0;
    }
    -----------------------------------------------------------------------
    -bash-3.2$ gcc -o output monthly_cost.c -lm
    -bash-3.2$ ./output

    Please, Enter the sq. Footage: 2600

    Now, Enter the Down Payment: 20000

    Please, Enter the monthly interest rate in percentage: 5.6

    please, Enter the annual number of payments: 12

    Your house cost is $46792.31
    Your cost after fuel cost is $46976.47
    Your monthly payment is $2316.81

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    There is a difference between interest/(12*100) and interest/12*100.

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    Good eye! The program looked alright to me.
    This might be questionable:
    Code:
    cost=sf*18-(down/sf)
    because sf can be factored out a bit. Just a thought. Could be ok. I just don't know what it was meant to do... or in general, where the program's output isn't what was expected.

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    Please, Enter the sq. Footage: 2600

    Now, Enter the Down Payment: 20000

    Please, Enter the monthly interest rate in percentage: 5.6
    that's if I change it to 12*100 still too low

    please, Enter the annual number of payments: 12

    Your house cost is $46792.31
    Your cost after fuel cost is $46976.47
    Your monthly payment is $1258902.14
    Last edited by beho86; 10-22-2008 at 06:44 PM.

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    hey nonoob,
    The numbers doesn't make sense for me, a house for 46 thousand and 2316 monthly!!!

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    I need the 100 to be divided as the user will enter it in percentage.

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    Ok, I don't have a good feel for what numbers sound good. You're using a lot of magic numbers like 18 and 0.85 so I couldn't begin to second-guess.

    For one thing you've asked for monthly interest, yet your program converts from yearly to monthly... so I wasn't sure which way it's expecting it.

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    You're right, the only thing that I am not sure about, when I add the fuel cost, should I add that to the monthly bill?!

  9. #9
    and the Hat of Guessing tabstop's Avatar
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    Since you're doing a one-year mortgage, 2316/month is probably about right. Perhaps you don't intend to do a one-year mortgage?

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    That's right, if I'm asking the user for annual number or payments, can he enter more than 12, or I should make it years. I don't know.

  11. #11
    and the Hat of Guessing tabstop's Avatar
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    It's your program.

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    okay, here's the main question that I was asked to do:
    Create a working program that will prompt the user for the necessary input information and display the monthly housing costs;

    Equations:
    Price = square footage * 18 - (down payment/square footage)

    Mortgage= iP/(1-(1+i)^(-n)
    i= monthly interest rate
    p=principle ( money you borrowed)
    n= number of payments ( 30 yr mortgage=360, 15 yr mortgage=180)

    annual Fuel cost = square footage * 0.85

  13. #13
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    Since monthly is assumed in the problem and the formulas, you don't need to ask for that, but you do need to ask for years.

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    Right Tabstop, I'll have to edit the whole program as I'm working in months, do you think the equations are right

  15. #15
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    All the formulas are in months. But they appear to be right.

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