COding help, output is wrong

Code:

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double getPaymentAmount(double interest, int numberOfMonths, double principal)
{
        double getPaymentAmount;
                getPaymentAmount = (powf((1+interest),numberOfMonths)/
                                                        (powf((1+interest),numberOfMonths)-1)
                                                        *principal*interest);
                                                       
        return getPaymentAmount;
}
//----------------------------------------------------------------------------
//
//----------------------------------------------------------------------------
double getLoanAmount(double interest, int numberOfMonths, double payment)
{
        double getLoanAmount;
                getLoanAmount = (powf((1+interest),numberOfMonths) - 1*payment)/
                                                (interest*powf((1+interest),numberOfMonths));

        return getLoanAmount;

}
//----------------------------------------------------------------------------
//
//----------------------------------------------------------------------------
int getNumberOfMonths(double interest, double payment, double principal)
{
        int getNumberOfMonths;
                getNumberOfMonths = (log(payment)-log(payment-(principal*interest))) /
                                                        (log(1+interest));

        return getNumberOfMonths;

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payment = (1 + i)^ months * principal * i

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(1 + i) months - 1


principal = (1 + i )^ months - 1 * payment

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i * (1 + i ) months


months = log( payment ) - log( payment - (principal * i ))

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log( 1 + i )

this is the regular formula. can someone tell me what im doing wrong here?

--------------------- means divide it by
(1+i)^months
-------------- * principal * i
(1+i)^months -1

ect,,,

What are the inputs and expected outputs? What are the actuals? Also this part of your formula doesn't make sense to me:

Quote:

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principal = (1 + i )^ months - 1 * payment

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Why would you be multiplying the payment by 1? It's not going to do anything. Should it be:

Quote:

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principal = (1 + i )^(months - 1) * payment

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??