Thread: monthly payment from math to C++

  1. 06-10-2010 #1
    summerwine
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    monthly payment from math to C++

    so my problem is that i really don't know how to convert the formula from this question into C++

    the monthly payment on a loan may be calculated by the formula

    payment = (Rate * (1+Rate)^N ) * Loan / ((1+Rate)^N - 1)

    rate is the monthly interest rate which is the annual interest rate divided by 12
    12% annula interest rate would be 1 percent monthly interest. N is the number of payments
    Loan is amount of loan
    write a program that asks for there values and displays a report similiar to:


    Loan amount: $ 10000.00
    Monthly Interest Rate: 1%
    Number of Payments: 36
    Monthly Payment: $ 332.14
    Amount Paid Back: $ 11957.15
    Interest Paid: $ 1957.15
  2. 06-10-2010 #2
    C_ntua
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    It would be exactly like that except that there is no ^ operator in C++. You can use the function pow(). You need to #include <math.h>
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  3. 06-10-2010 #3
    summerwine
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    so what hurts me here, is that i did it with power function.
    and it's not working at all.
  4. 06-10-2010 #4
    summerwine
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    that's what i have

    Payment = (Monthly_Interest_Rate * pow(1 + Monthly_Interest_Rate, Number_Of_Payments)) * Loan /( pow(1+Monthly_Interest_Rate, Number_Of_Payments) - 1) ;
  5. 06-10-2010 #5
    x2x3i5x
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    is this what you're looking for?

    I used the following formula in my program and with my code, it shows a monthly payment of 332.14 given the 10000.00 amount like your sample output wants.

    Code:
    payment_amt = (loan_amt * monthy_interest_rate) / (1 - pow(1+monthy_interest_rate,-loan_term_months));

    Quote Originally Posted by C_ntua View Post
    You need to #include <math.h>
    Actually, use the #include <cmath> preprocessor directive. math.h is the old style math header for C++.
    Last edited by x2x3i5x; 06-10-2010 at 09:38 PM.
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