javascript - Javascript 年复利计算

Question

当此代码运行时，它会为每一年输出“年度 (i) = 100 的年度账户余额”。显然答案不应该每次都是 100，但我看不出我在等式中做错了什么。

var invest;
var rate;
var amount; 

rate = 0.08;
invest = 100,000;

    for(var i=1;i<=10;i++){
        amount = ((parseInt(invest)) * (1.0 + (parseInt(rate)) * (parseInt(i))))
        document.write("Annual Account Balance for Year " + i + " = " + amount + "<br>");
    }

Answer 1

parseInt(rate)您需要调用而不是调用parseFloat(rate)- 尽管根据您的代码，这些是数字 - 所以无论如何都不需要解析它们。

parseInt将从字符串中解析一个整数（尽管它仍然是“数字”类型）。在这种情况下，它实际上返回 0 而不是您要使用的 0.08。调用parseInt一个数字会将其从一个数字转换为一个字符串，然后再返回......这基本上是无用的。

此外，正如 Oriol 所说，您不能在 JavaScript 中为数字添加逗号。

Answer 2

parseInt(0.08)给出0所以数学没有做任何事情。您无需在此处解析变量，因为您自己定义了它们。如果你从用户输入中读取，你真的只需要解析。

你的兴趣数学也很糟糕。您需要计算利息而不是利息。

此脚本提供正确的*输出：

var invest;
var rate;
var amount; 

rate = 0.08;
invest = 100000;

amount = invest;
for(var i = 1; i <= 10; i++){
    amount = amount * (1.0 + rate);
    document.write("Annual Account Balance for Year " + i + " = " + amount + "<br>");
}

输出：

Annual Account Balance for Year 1 = 108000
Annual Account Balance for Year 2 = 116640.00000000001
Annual Account Balance for Year 3 = 125971.20000000003
Annual Account Balance for Year 4 = 136048.89600000004
Annual Account Balance for Year 5 = 146932.80768000006
Annual Account Balance for Year 6 = 158687.43229440006
Annual Account Balance for Year 7 = 171382.42687795206
Annual Account Balance for Year 8 = 185093.02102818823
Annual Account Balance for Year 9 = 199900.4627104433
Annual Account Balance for Year 10 = 215892.49972727877

// this would be the output with your bad math:

Annual Account Balance for Year 1 = 108000
Annual Account Balance for Year 2 = 115999.99999999999 // float funny business, beware!
Annual Account Balance for Year 3 = 124000
Annual Account Balance for Year 4 = 132000
Annual Account Balance for Year 5 = 140000
Annual Account Balance for Year 6 = 148000
Annual Account Balance for Year 7 = 156000
Annual Account Balance for Year 8 = 164000
Annual Account Balance for Year 9 = 172000
Annual Account Balance for Year 10 = 180000

* 因为我们在这里处理浮点值，所以要非常小心它的有限精度。