Question

first off this is a class assignment so i would appreciate help but just hints as i want to learn. I have to calculate monthly payment based off of interest rate etc as seen in my code but something is off with my calculation. My output reads nan which i believe is not a number. I have been trying to figure out where i am going wrong to no avail,any suggestions on how to correct this issue? Thanks in advance.

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main()
{
    //collect payment info
    double loanAmount = 0; 
    double anualRate = 0;
    double monthlyIntRate = 0; 
    int numOfPayment = 0; 
    double monthlyPayment = 0; 
    double amountPaidBack = 0; 
    double interestPaid = 0;

    cout << "Enter loan amount: ";
    cin >> loanAmount;
    cout << "Enter Anual Interest Rate: ";
    cin >> anualRate;
    cout << "Enter Payments made: ";
    cin >> numOfPayment;

    //calculate montly payment
    monthlyPayment = (loanAmount * pow(monthlyIntRate + 1, numOfPayment) * monthlyIntRate) / ( pow(monthlyIntRate + 1, numOfPayment) - 1);                                                    

    //calculate amount paid back
    amountPaidBack = monthlyPayment * numOfPayment;

    //calculate interest paid
    monthlyIntRate = anualRate / 12;
    interestPaid = monthlyIntRate * numOfPayment;

    //split input from calculated output
    cout << "-----------------------------\n" << endl;

    //Display the calulated data
    cout << fixed;
    cout << setprecision(2);

    cout << "Loan Amount: " << setw(15) << "$ "<< right << loanAmount << endl;

    cout << "Monthly Interest Rate: " << setw(14) << monthlyIntRate << "%" << endl;

    cout << "Number of Payments: " << setw(17) << numOfPayment << endl;

    cout << "Montly Payment: " << setw(19) << "$ " << monthlyPayment << endl;

    cout << "Amount Paid Back: " << setw(17) << "$ " << amountPaidBack << endl;

    cout << "Interest Paid: " << setw(18) << "$ " << interestPaid << endl;

    return 0;

Output:

Loan Amount:              $ 100000.00
Monthly Interest Rate:           1.00%
Number of Payments:                36
Montly Payment:                  $ nan
Amount Paid Back:                $ nan
Interest Paid:                 $ 36.00

Answer 1

You’re dividing by zero. it occurs in this line:

monthlyPayment = (loanAmount * pow(monthlyIntRate + 1, numOfPayment) * monthlyIntRate) / ( pow(monthlyIntRate + 1, numOfPayment) - 1);

The value stored in monthlyIntRate is zero, so pow(monthlyIntRate + 1, numOfPayment) eqauls to (0 + 1) ^ numOfPayment, which is 1. So, pow(monthlyIntRate + 1, numOfPayment) - 1) is 0.