贷款计算器公式错误C＃[关闭]

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace IndividualAssignmentLoan {

public partial class WebForm1 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        jmToday.Caption = Format(Now, "DDDD, D/MMMM/YYYY")
    }

    protected void btnCalculate_Click(object sender, EventArgs e)
    {
        double amount = double.Parse(jmLoanAmount.Text);
        double downPay = double.Parse(jmDownPayment.Text);
        double interest = double.Parse(jmInterestRate.Text);
        int period = int.Parse(jmLoanPeriod.Text);

        Double monthlyPay;
        Double loanCost;

        monthlyPay = ((amount * interest) / 1) - (Math.Pow(1/(1 + interest), period));
        loanCost = monthlyPay * (period * 12);

        jmMonthlyPayment.Text = monthlyPay.ToString();
        jmTotalLoanCost.Text = loanCost.ToString();
    }
}
}

嗨，我已写到我不明白我的贷款计算器出错的地方。我已输入我的公式以获得贷款金额......

monthlyPay = ((amount * interest) / 1) - (Math.Pow(1/(1 + interest), period));

我已经尝试了其他方法来获得正确的金额，但似乎没有什么能给我每月需要的金额。有人可以帮我配方。哦，我的时钟，我有顶级大声笑...

jmToday.Caption = Format(Now, "DDDD, D/MMMM/YYYY")

Answer 1

当教师教学生使用双倍与金钱相关的操作时，我讨厌它。总是使用小数，小孩！ 128位非浮点优点（https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/decimal）

无论如何，我认为我破解了你的老师对公式的意图（你的评论至少可以说是模棱两可的）。我想你想要：

double actualAmountToPay = amount - downPay;
double monthlyPay = actualAmountToPay * interest / (1 - 1 / Math.Pow((1 + interest), period));
double totalCost = monthlyPay * (period * 12);

Answer 2

保留btnClick处理解析并将每月付款计算移至单独的方法：

double CalculateMonthlyPayment(double amount, double downPayment, int termInYears, double interestRate)
{
    int paymentsCount = MonthsPerYear * termInYears;
    double principal = amount - downPayment;

    if (interestRate == 0)
    {
        return principal / paymentsCount;
    }

    double monthlyRate = interestRate / MonthsPerYear;
    double coefficient = Math.Pow(1 + monthlyRate, paymentsCount);
    double monthlyPayment = principal * (monthlyRate * coefficient) / (coefficient - 1);

    return monthlyPayment;
}

MonthsPerYear是一个具有明显价值的常数。

TotalPayment将是paymentsCount * MonthlyPayment

请记住，您需要处理异常情况：amount <= 0，downPayment < 0，amount <= downPayment，termInMonths < 1。还要决定是否允许负利率。