c++ - 计算汽车付款金额计算不正确

Question

我正在为家庭作业创建一个小程序。程序运行正常，只是计算不正确。

我用来计算付款金额的公式是:

付款 = (intRate * (1+intRate)^N/((1+intRate)^N-1)) * L

其中“N”是付款次数，“L”是本金。我为此编写的代码是:

monthlyPayment = (intRate * pow ((1 + intRate), numberPayments) / (intRate * pow ((1 +     intRate), numberPayments)-1))*principal;

完整代码如下。

#include <iostream>
#include <string>
#include <cmath>
#include <iomanip>

using namespace std;

int main()
{
    double principal, intRate, paybackAmount, interestPaid,  monthlyPayment;
    int numberPayments;

    // Change the panel color.
    system ("color F0");

    cout << "\n";
    cout << "This application will calculate your loan amounts." << endl;
    cout << "Please enter the data below." << endl;
    cout << "\n";

    cout << "Loan Amount: ";
    cin >> principal;
    cout << "Monthly Interest Rate: ";
    cin >> intRate;
    cout << "Number of Payments: ";
    cin >> numberPayments;


    cout << "\n\n\n";

    monthlyPayment = (intRate * pow ((1 + intRate), numberPayments) / (intRate *     pow ((1 + intRate), numberPayments)-1))*principal;
    paybackAmount = monthlyPayment * numberPayments;

    cout << fixed << setprecision(2) << showpoint << left << setw(24) << "Loan     Amount:" << "$" << setw(11) << right << principal << endl;
    cout << fixed << setprecision(1) << showpoint<< left << setw(24) << "Monthly     Interest Rate:" << setw(11) << right << intRate << "%" << endl;
    cout << fixed << setprecision(0) << left << setw(24) << "Number of Payments:"     << setw(12) << right << numberPayments << endl;
    cout << fixed << setprecision(2) << showpoint<< left << setw(24) << "Monthly     Payment:" << "$" << setw(11) << right << monthlyPayment << endl;
    cout << fixed << setprecision(2) << showpoint<< left << setw(24) << "Amount     Paid Back:" << "$" << setw(11) << right << paybackAmount << endl;
    cout << fixed << setprecision(2) << showpoint<< left << setw(24) << "Interest     Paid:" << "$" << right << setw(11) << paybackAmount - principal << "\n\n" << endl;


    system("pause");
}

在此先感谢您的帮助!

Answer 1

您将分子和分母都乘以 intRate，而根据您的等式，您应该只乘以分子。

您还从第二个 pow 的结果中减去 1，而不是从 numberPayments 中减去。

(intRate * pow ((1 + intRate), numberPayments)-1)
//  ^ Why is this here?            Wrong place ^

你真正想要的是:

monthlyPayment = (intRate * pow(1+intRate, numberPayments) /
                            pow(1+intRate, numberPayments-1)) * principal;