C Programming using vi editor :(

[canteyn]

I am currently working on a lab for my computer science class, and we are to write program (using a function) to calculate the monthly payment. We also are reading the principal loan, interest rate, and number of payments from a file, and then passing this values to the function which returns the "monthly payment". Then we write the monthly payment to another file. After this we end the program.

Here is what I have so far. My problem is when I open the file to see if my program wrote the correct monthly payment. When I read the file I see "The monthly payment is $NaN". I know this is telling me that it is not receiving a correct number and that is what the "NaN" is representing, but my question is why. Someone please look at this code and tell me what I might have done wrong. Thank you!

#include <stdio.h> /* preprocessor directive for printf, scanf */
#include <math.h>  /* preprocessor directive for math operators */
 
double calculatePayment ( );
 
main ()
 
{
     double Princ, interest, n, monthlyPayment, mI; /* variables for main */
     FILE* in; /* assigns in as a file pointer */
     FILE* out; /* assings out as a file pointer */
 
    /* open files */
    in = fopen( "lab2.in", "r" );
 
    /* read in principal, annual interest rate, and total number of payments */
    fscanf ( in, "%f%f%f", &Princ, &interest, &n);
    fclose(in);
 
    mI = interest / 12;
 
    /* call calculatePayment to receive payment ammount */
    monthlyPayment = calculatePayment( Princ, mI, n);
 
    /* write monthlyPayment to lab2.out file */
    out = fopen ( "lab2.out", "w" );
    fprintf( out, "The monthly payment is $%.2lf", monthlyPayment );
 
    /* close files, end program */
    fclose(out);
    return(0);
}
    /*
         Function name:  calculatePayment
         Parameters:  Principal loan ammount, interest rate, number of payments
         Returns:  Monthly payment for loan
    */
 
    /* Function heading */
    double calculatePayment ( double Principal, double monthlyInterest, double numberPayments)
{
 
    double payment;
 
    payment = (monthlyInterest*Principal)/(pow(1-(1+monthlyInterest), numberPayments))*-1;
 
    return (payment);
}
 

[sicarie]

I am currently working on a lab for my computer science class, and we are to write program (using a function) to calculate the monthly payment. We also are reading the principal loan, interest rate, and number of payments from a file, and then passing this values to the function which returns the "monthly payment". Then we write the monthly payment to another file. After this we end the program.

Here is what I have so far. My problem is when I open the file to see if my program wrote the correct monthly payment. When I read the file I see "The monthly payment is $NaN". I know this is telling me that it is not receiving a correct number and that is what the "NaN" is representing, but my question is why. Someone please look at this code and tell me what I might have done wrong. Thank you!

#include <stdio.h> /* preprocessor directive for printf, scanf */
#include <math.h>  /* preprocessor directive for math operators */
 
double calculatePayment ( );
 
main ()
 
{
     double Princ, interest, n, monthlyPayment, mI; /* variables for main */
     FILE* in; /* assigns in as a file pointer */
     FILE* out; /* assings out as a file pointer */
 
    /* open files */
    in = fopen( "lab2.in", "r" );
 
    /* read in principal, annual interest rate, and total number of payments */
    fscanf ( in, "%f%f%f", &Princ, &interest, &n);
    fclose(in);
 
    mI = interest / 12;
 
    /* call calculatePayment to receive payment ammount */
    monthlyPayment = calculatePayment( Princ, mI, n);
 
    /* write monthlyPayment to lab2.out file */
    out = fopen ( "lab2.out", "w" );
    fprintf( out, "The monthly payment is $%.2lf", monthlyPayment );
 
    /* close files, end program */
    fclose(out);
    return(0);
}
    /*
         Function name:  calculatePayment
         Parameters:  Principal loan ammount, interest rate, number of payments
         Returns:  Monthly payment for loan
    */
 
    /* Function heading */
    double calculatePayment ( double Principal, double monthlyInterest, double numberPayments)
{
 
    double payment;
 
    payment = (monthlyInterest*Principal)/(pow(1-(1+monthlyInterest), numberPayments))*-1;
 
    return (payment);
}
 

One of the first things I see (before I compile), is that you return a 0 to main. If you do this, you need to use 'int main() ' at the intro to main.

(Also, if you could use the code tags - they are [ code] and [ /code] (without the spaces), it makes your program much easier to read. Thanks!)

[sicarie]

One of the first things I see (before I compile), is that you return a 0 to main. If you do this, you need to use 'int main() ' at the intro to main.

(Also, if you could use the code tags - they are [ code] and [ /code] (without the spaces), it makes your program much easier to read. Thanks!)

And from there, the error is in your "pow" statement. (hint: count the parentheses)

[canteyn]

And from there, the error is in your "pow" statement. (hint: count the parentheses)

when I counted it seemed to be fine, but I did recognize that I did not have one to close the "x value" in my pow statement ( pow(x, y) ). I corrected that, but now it gives me an error stating that I have to few arguments.

[sicarie]

when I counted it seemed to be fine, but I did recognize that I did not have one to close the "x value" in my pow statement ( pow(x, y) ). I corrected that, but now it gives me an error stating that I have to few arguments.

Apologies - I should have said 'by the pow statement' I didn't know where you wanted to end it - can you post the new pow statement (so we're both working with the same code)?

[RedSon]

Please post your build output so we can see the error.

[canteyn]

when I counted it seemed to be fine, but I did recognize that I did not have one to close the "x value" in my pow statement ( pow(x, y) ). I corrected that, but now it gives me an error stating that I have to few arguments.

ok I am an idiot, I just fixed the argument issue, but I am still receiving NaN in my output file.

[RedSon]

When you debug this what is your monthlyPayment after the call to calculatePayment? If it is a valid number then your problem is in fprintf( out, "The monthly payment is $%.2lf", monthlyPayment );

[canteyn]

    /*
         Function name:  calculatePayment
         Parameters:  Principal loan ammount, interest rate, number of payments
         Returns:  Monthly payment for loan
    */
 
    /* Function heading */
    double calculatePayment ( double Principal, double monthlyInterest, double numberPayments)
{
 
    double payment;
 
    payment = (monthlyInterest*Principal)/pow((1-(1+monthlyInterest)), numberPayments)*-1;
 
    return (payment);
}
 

here is the function including pow statement as it is currently.


When I compile I am typing

"gcc lab2.c -lm"

and then I am checking the "lab2.out" file for the result, which in the file states

"The monthly payment is $NaN"

Is that what you were asking for Redson?

[sicarie]

    /*
         Function name:  calculatePayment
         Parameters:  Principal loan ammount, interest rate, number of payments
         Returns:  Monthly payment for loan
    */
 
    /* Function heading */
    double calculatePayment ( double Principal, double monthlyInterest, double numberPayments)
{
 
    double payment;
 
    payment = (monthlyInterest*Principal)/pow((1-(1+monthlyInterest)), numberPayments)*-1;
 
    return (payment);
}
 

here is the function including pow statement as it is currently.


When I compile I am typing

"gcc lab2.c -lm"

and then I am checking the "lab2.out" file for the result, which in the file states

"The monthly payment is $NaN"

Is that what you were asking for Redson?

I'm guessing that you're overflowing. Can you calculate the parts separately, and output them to see if they're correct?

[RedSon]

    /*
         Function name:  calculatePayment
         Parameters:  Principal loan ammount, interest rate, number of payments
         Returns:  Monthly payment for loan
    */
 
    /* Function heading */
    double calculatePayment ( double Principal, double monthlyInterest, double numberPayments)
{
 
    double payment;
 
    payment = (monthlyInterest*Principal)/pow((1-(1+monthlyInterest)), numberPayments)*-1;
 
    return (payment);
}
 

here is the function including pow statement as it is currently.


When I compile I am typing

"gcc lab2.c -lm"

and then I am checking the "lab2.out" file for the result, which in the file states

"The monthly payment is $NaN"

Is that what you were asking for Redson?

No I want the output from gcc try using the verbose flag to see all the compiler junk. But don't worry about it now you fixed the complier problems so I don't need to see the compiler output.

[sicarie]

I'm still getting 'undefined reference to pow()'.

[canteyn]

yea there is something wrong with my function, I am pretty sure of that. However, I have no idea where is the world it is messing up, because I am pretty sure that it is not returning the proper value back to my main code, I am at a complete loss.

[sicarie]

yea there is something wrong with my function, I am pretty sure of that. However, I have no idea where is the world it is messing up, because I am pretty sure that it is not returning the proper value back to my main code, I am at a complete loss.

So what is your algorithm for calculating the payment? (maybe we can work through it and find the error or find a workaround)

[RedSon]

Have you stepped through you code using a debugger to see what is going on?

[canteyn]

I am unsure on how to debug at all I am sorry.

My algorithm is as follows

1. Open file lab2.in
2. Read in principal loan
3. Read in annual interest rate
4. Read in total number of payments
5. Close file lab2.in
6. monthlyInterest = annualrate / 12
7. Call “calculatePayment” function to calculate
8. Read in “payment” from “calculatePayment” function
9. Open file lab2.out
10. Write the results of “calculatePayment” function to file
11. Close file lab2.out
12. Close program

Lab 2 Function Algorithm (calculatePayment)

1. Parameters: P = principal, i = monthly interest rate, n = total number of payments (number of months in payment term)
2. Read in principal loan, annual interest rate, total number of payments
3. Calculate to find loan payment:

iP
Payment = ------------
(1-(1+i) ‾ ⁿ
4. Return “payment” to main


My data in the "lab2.in" file reads as follows:

18300 0.0575 36

My data in the "lab2.out" file SHOULD read as follows:

The monthly payment is $554.65

but is $NaN

[RedSon]

I'm not sure how to debug using gcc. You might try googling on that, being able to use a debugger is invaluable when trying to solve problems.

[canteyn]

I'm not sure how to debug using gcc. You might try googling on that, being able to use a debugger is invaluable when trying to solve problems.

I agree I hate gcc!

[nmadct]

I'm not sure how to debug using gcc. You might try googling on that, being able to use a debugger is invaluable when trying to solve problems.

To debug with gcc, the first step is to compile with the -g switch to turn on debugging.

The most basic way to debug is using gdb, the command-line debugger. It's powerful enough but has a steep learning curve.

The other way is using an IDE, you can try KDevelop on Linux or DevC++ on Windows. I believe these actually use gdb as the backend for their debuggers.

[nmadct]

Also, there's a graphical front-end to gcc, it's called ddd. Probably not as convenient as a full IDE but easier and faster than gdb.

[RedSon]

I agree I hate gcc!

LOL I didnt say I hated gcc!

[canteyn]

LOL I didnt say I hated gcc!

ok well I said I hate gcc :)

and I have to turn this in in 1 hour, lol, this is not looking so well for me.

[sicarie]

ok well I said I hate gcc :)

and I have to turn this in in 1 hour, lol, this is not looking so well for me.

I think you're mixing up order of operations (I was wondering why you were adding 1 and then subtracting one right away).

Can you do the operations one step at a time?

[sicarie]

(For example: )

payment = 1+monthlyInterest;
 
payment = pow(payment, n);
 
payment = 1 - payment;
 

[canteyn]

(For example: )

payment = 1+monthlyInterest;
 
payment = pow(payment, n);
 
payment = 1 - payment;
 

Ok well I tried that, and I am no longer getting $NaN, rather now I am getting $-0.00

[sicarie]

Ok well I tried that, and I am no longer getting $NaN, rather now I am getting $-0.00

Did you do outputs after each one to see if they were computing the correct numbers (if they were even getting passed correctly)?

[DeMan]

my apologies if someone already suggested it but BEWARE the implicit cast......

If you are calculating with doubles use values like 1.0 rather than 1, otherwise funny things might happen when the compiler tries to "fix" what you're doing