java每年将复合利息转为每月

Question

我需要做的是提示用户提供本金，利率和期限。然后用户选择数月或数年。

我不知道如何使用for循环计算复合月利率。我已经在线查看了公式，但每当我尝试将其翻译成java代码时，我都会失败。

我知道我需要除以12，但在循环中我的利息和本金金额一直变小，直到0.有人可以帮忙吗？ ty

 public Calculator()
{
    Scanner input = new Scanner(System.in);
    boolean error = false;

    while (!error){
    System.out.print("Please input the following: principal, interest rate, term >> ");
    double principal = input.nextDouble();
    double interest_rate = input.nextDouble(); 
    int term = input.nextInt();
    String MonthOrYear = input.next();

    int termInMonths = term * 12;


    char dollar_sym = 36;


    if (interest_rate <= 0 || term <= 0 || principal <= 0)
    {
     System.out.println("The term, interest rate and principal must be greater than zero");
     continue; 
    }
    if (!MonthOrYear.equals("month") && (!MonthOrYear.equals("year")&&
    (!MonthOrYear.equals("Month")&& (!MonthOrYear.equals("Year") && (!MonthOrYear.equals("years")
    && (!MonthOrYear.equals("months") && (!MonthOrYear.equals("Years") && 
    (!MonthOrYear.equals("Months")))))))))
    {
     System.out.println("Please input either month or year after term"); 
     continue; 
    }

    System.out.println("Month: " + "  Interest: " + "Principal:  "); 

    if (MonthOrYear.equals("month") || (MonthOrYear.equals("Months") || (MonthOrYear.equals("Month")
    || (MonthOrYear.equals("months")))))
    {
       for (int month = 1; month <= term; month++)
       { 
       double interest = principal * interest_rate / 100;
       principal = principal + interest; 
       System.out.printf("%4d      %c%5.2f    %c%5.2f\n", month, dollar_sym, interest, dollar_sym, principal );

      }

    }
    else if (MonthOrYear.equals("year") || (MonthOrYear.equals("Years") || (MonthOrYear.equals("Year")
    || (MonthOrYear.equals("years")))))
    {

       for (int month = 1; termInMonths >= month; month++)
       { 
       double interest = principal * interest_rate / 100;
       principal = principal + interest; 
       System.out.printf("%4d      %c%5.2f    %c%5.2f\n", month, dollar_sym, interest, dollar_sym, principal );
      }

    }

   break;