Function

Hi guys: This is a program with one return function name getPayment.

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace test;
double getPayment(int, double, int);
void displayPayment(void);
int main()
{
      int carPrice = 0;
      int rebate = 0;
      double creditRate = 0.0;
      double dealerRate = 0.0;
      int term = 0;
      double creditPayment = 0.0;
      double dealerPayment = 0.0;

      cout << "Car price (after any trade-in):";
      cin >> carPrice;
      cout << "Rebate:";
      cin >> rebate;
      cout << "Credit union rate:";
      cin >> creditRate;
      cout << "Dealer rate:";
      cin >> dealerRate;
      cout << "Term in years:";
      cin >> term;
      displayPayment();
      creditPayment = getPayment(carPrice - rebate, creditRate / 12, term * 12);
      dealerPayment = getPayment(carPrice, dealerRate / 12, term * 12);
      cout << fixed << setprecision(2) << endl;
      cout << "Credit union payment: " << creditPayment << endl;
      cout << "Dealer payment: $" << dealerPayment << endl;
      system("pause");
      return 0;
}

double getPayment(int prin, double monthRate, int months)
{
      double monthPay = 0.0;
      monthPay = prin * monthRate / (1 - pow(monthRate + 1, -months));
      return monthPay;
}

void displayPayment(void)
{
      int monthlyPayment = 0;
      cout << "Enter monthly payment-->";
      cin >> monthlyPayment;
      cout << "Monthly Payment-->" << monthlyPayment << endl;
}
----------------------------------------------------------------
I change the getPayment function with void calcPayment(void) function but did mistake in the calculation of creditpayment and dealer payment. Can any one please help me out ? Thanks.

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace test;
void CalcPayment(void);
void displayPayment(void);
int main()
{
      CalcPayment();
      system("pause");
      return 0;
}

void CalcPayment(void)
{
      double creditPayment = 0.0;
      double dealerPayment = 0.0;
      double monthPay = 0.0;
      int carPrice = 0;
      int rebate = 0;
      double creditRate = 0.0;
      double dealerRate = 0.0;
      int term = 0;
      int prin = 0;
      double monthRate = 0.0;
      int months = 0;
      cout << "Car price (after any trade-in):";
      cin >> carPrice;
      cout << "Rebate:";
      cin >> rebate;
      cout << "Credit union rate:";
      cin >> creditRate;
      cout << "Dealer rate:";
      cin >> dealerRate;
      cout << "Term in years:";
      cin >> term;
      displayPayment();
      //creditPayment = carPrice - rebate, creditRate / 12, term * 12;
      //dealerPayment = carPrice, dealerRate / 12, term * 12;
      monthRate = creditRate / 12;
      months = term * 12;
      creditPayment = (carPrice - rebate) * monthRate / (1 - pow(monthRate + 1, -months));
      dealerPayment = carPrice * monthRate / (1 - pow(monthRate + 1, -months));
      cout << fixed << setprecision(2) << endl;
      cout << "Credit union payment: " << creditPayment << endl;
      cout << "Dealer payment: $" << dealerPayment << endl;

}


void displayPayment()
{
      int monthlyPayment = 0;
      cout << "Enter monthly payment-->";
      cin >> monthlyPayment;
      cout << "Monthly Payments-->" << monthlyPayment << endl;
}