java我如何计算和显示未来5年每一年的投资价值

Question

我相信我在这里犯了一个数学公式错误，代码似乎是有效的，但是数学结果完全错误了

   public static void main (String [] args) {
       
       Scanner sam = new Scanner(System.in);
       
       System.out.print("enter initial investment: ");
       double principal = sam.nextDouble();
       System.out.print("enter initial rate:  ");
       double Rate = sam.nextDouble();
       System.out.print("Enter the time:  ");
       double time = sam.nextDouble();
       Rate = (1 + (Rate / 100));
       double interest = (principal * Rate);
       for (int i=1; i < time; i++) {
           System.out.printf("year %d \n", i);
           System.out.printf("interest: %f \n", interest);
           double amount = (principal + interest);
           interest = (amount * Rate);
           System.out.printf("value: %f \n", amount);
       }
    }

输出：

enter initial investment: 1000
enter initial rate:  5
Enter the time:  5
year 1 
interest: 1050.000000 
value: 2050.000000 
year 2 
interest: 2152.500000 
value: 3152.500000 
year 3 
interest: 3310.125000 
value: 4310.125000 
year 4 
interest: 4525.631250 
value: 5525.631250

Answer 1

问题似乎在于将比率设置为1 + Rate / 100，即比率超过100%。此外，利息没有适当地计入本金

另外，最好避免在货币算术中使用double

因此，固定代码可能如下所示：

       Scanner sam = new Scanner(System.in);
       
       System.out.print("enter initial investment: ");
       int principal = sam.nextInt() * 100; // in cents
       System.out.print("enter initial rate:  ");
       int Rate = sam.nextInt(); // percent
       System.out.print("Enter the time:  ");
       int time = sam.nextInt();
       
       int interest = (principal * Rate) / 100;
       for (int i=1; i < time; i++) {
           System.out.printf("year %d \n", i);
           System.out.printf("interest: %s \n", interest / 100.0);
           principal += interest; // adding interest
           interest = (principal * Rate) / 100;
           System.out.printf("value: %s\n", principal / 100.0);
       }

输出

enter initial investment: 1000
enter initial rate:  5
Enter the time:  5
year 1 
interest: 50.0 
value: 1050.0
year 2 
interest: 52.5 
value: 1102.5
year 3 
interest: 55.12 
value: 1157.62
year 4 
interest: 57.88 
value: 1215.5

Answer 2

好吧，多亏了@alex rudenko的回答，我成功地解决了这个问题 '''

   Scanner sam = new Scanner(System.in);
   
   System.out.print("enter initial investment: ");
   double principal = sam.nextDouble();
   System.out.print("enter initial rate:  ");
   double Rate = sam.nextDouble();
   System.out.print("Enter the time:  ");
   double time = sam.nextDouble();
   Rate /= 100.0;
   double interest = (principal * Rate);
   for (int i=1; i < time; i++) {
       System.out.printf("year %d \n", i);
       System.out.printf("interest: %f \n", interest);
       principal  = (principal + interest);
       interest = (principal*Rate); 
       System.out.printf("value: %f \n", principal);
   }
}

'''

输出： 输入初始投资：1000 输入初始速率：5 输入时间：5 第一年 利息：50.000000 价值：1050.000000 第二年 利息：52.500000 价值：1102.500000 第三年 利息：55.125000 价值：1157.625000 第四年 利息：57.881250 数值：1215.506250