每月摊销计算器中的循环在 0 之后运行 [Java]

Question

我几乎完成了一个基于用户本金、每月利息和每月还款额的每月摊还计算器的编程。但是最后一个问题我似乎无法弄清楚。我似乎已将限制设置为 0，但如果是负资金，它仍会显示第一个金额。这是为了更好地理解我的意思的代码：

import java.util.Scanner;

public class Amortization {

   public static void main(String []args){

       Scanner input = new Scanner(System.in);
       int month = 1;
       int year = 0;

       double balance;
       double rate;
       double payment;
       double principal;
       double calculated_interest;
       double actual_payment;
       double principal_amt;

       System.out.println("What is your principal amount?"); principal = input.nextDouble(); balance = principal;
       System.out.println("What is your monthly interest rate in decimal?"); rate = input.nextDouble();
       System.out.println("What is your monthly payment?"); payment = input.nextDouble();


       while(balance>0){

          if(month == 13){
             year++;
             month = 1;
          }

          calculated_interest = ((int)(Math.round(balance*rate*100)))/100.0;
          principal_amt = ((int)(Math.round((payment-calculated_interest))*100))/100.0;
          actual_payment = ((int)(Math.round((payment-calculated_interest)*100)))/100.0;

          System.out.println("Year " + year + ", " + "Month " + month + ":");
          System.out.println("Your interest amount is " + "$" + calculated_interest);
          System.out.println("Your principal amount " + "$" + principal_amt);
          balance = ((int)(Math.round((balance-actual_payment)*100)))/100.0;

          System.out.println("Your new balance is " + "$" + balance);
          System.out.println();

          month++;
      }
      input.close();
     }
  }

Answer 1

问题是当循环在第 29 年第 12 个月时，值是

Year 29, Month 12:
Your interest amount is $20.9
Your principal amount $4176.0
Your new balance is $3.45

现在，此时balance 的值不小于0，因此while 将为真，当计算新值时，余额(balance = ((int)(Math.round((balance-actual_payment)*100)))/100.0;) 变为负数，即balance - atual_payment will return negative because the previous balance is $3.45。

其中一种解决方案，在计算完余额后在while循环中添加另一个if条件。

while(balance>0){

      calculated_interest = ((int)(Math.round(balance*rate*100)))/100.0;
      principal_amt = ((int)(Math.round((payment-calculated_interest))*100))/100.0;
      actual_payment = ((int)(Math.round((payment-calculated_interest)*100)))/100.0;
      balance = ((int)(Math.round((balance-actual_payment)*100)))/100.0;

      if (balance < 0){
        break; //this will break out of the loop
      }

      if(month == 13){
         year++;
         month = 1;
      }
      System.out.println("Year " + year + ", " + "Month " + month + ":");
      System.out.println("Your interest amount is " + "$" + calculated_interest);
      System.out.println("Your principal amount " + "$" + principal_amt);

      System.out.println("Your new balance is " + "$" + balance);
      System.out.println();

      month++;
  }

此代码不会打印出负余额。

Answer 2

您的代码几乎没有问题。

• 每个月的利息和本金之和不等于每月还款。
• 不需要您计算的“actual_payment”。
• 您无需将付款四舍五入为整数。

• 因为您从用户那里收取每月付款，所以用户在上个月支付的每月付款将少于每月付款，这就是导致 -ve 如果您希望每个月的付款相等，您必须自己计算每月付款.

  public static void main(String[] args) {
      Scanner input = new Scanner(System.in);
      int month = 1;
      int year = 0;
  
      double balance;
      double rate;
      double payment;
      double principal;
      double calculated_interest;
      double actual_payment;
      double principal_amt;
  
      System.out.println("What is your principal amount?");
      principal = input.nextDouble();
      balance = principal;
      System.out.println("What is your monthly interest rate in decimal?");
      rate = input.nextDouble();
      System.out.println("What is your monthly payment?");
      payment = input.nextDouble();
  
      while (balance > 0) {
  
          if (month == 13) {
              year++;
              month = 1;
          }
          calculated_interest = (balance * rate * 100) / 100.0;
          principal_amt = payment - calculated_interest;
  
          System.out.println("Year " + year + ", " + "Month " + month + ":");
          System.out.println("Your interest amount is " + "$" + calculated_interest);
  
          if (balance > payment) {
  
              balance = ((int) (Math.round((balance - principal_amt) * 100))) / 100.0;
              System.out.println("Your principal amount " + "$" + principal_amt);
              System.out.println("Your new balance is " + "$" + balance);
          } else {
              System.out.println("Your principal amount " + "$" + (balance - calculated_interest));
              System.out.println("Your new balance is " + "$" + 0);
              System.out.println("You'll only pay $" + (calculated_interest + balance) + " this month.");
              break;
          }
  
          System.out.println();
  
          month++;
      }
      input.close();
  }