Java Double value = 0.01更改为0.009999999999999787 [英] Java Double value = 0.01 changes to 0.009999999999999787

问题描述

可能重复：

为什么不使用Double或Float来表示货币？

我正在为我的高中课程在Java中编写一个基本的命令行程序。我们现在只使用变量。用于在购买之后计算您更改中的任何类型的纸币和硬币的数量。这是我的程序：

I'm writing a basic command-line program in Java for my high school course. We're only working with variables right now. It's used to calculate the amount of bills and coins of whatever type in your change after a purchase. This is my program:

class Assign2c {
    public static void main(String[] args) {
        double cost = 10.990;
        int paid = 20;
        double change = paid - cost;
        int five, toonie, loonies, quarter, dime, nickel, penny;

        five = (int)(change / 5.0);
        change -= five * 5.0;

        toonie = (int)(change / 2.0);
        change -= toonie * 2.0;

        loonies = (int)change;
        change -= loonies;

        quarter = (int)(change / 0.25);
        change -= quarter * 0.25;

        dime = (int)(change / 0.1);
        change -= dime * 0.1;

        nickel = (int)(change / 0.05);
        change -= nickel * 0.05;

        penny = (int)(change * 100);
        change -= penny * 0.01;

        System.out.println("$5   :" + five);
        System.out.println("$2   :" + toonie);
        System.out.println("$1   :" + loonies);
        System.out.println("$0.25:" + quarter);
        System.out.println("$0.10:" + dime);
        System.out.println("$0.05:" + nickel);
        System.out.println("$0.01:" + penny);
    }
}

它应该都工作，但最后一步，当有剩下的$ 0.01，便士的数量应该是1，而是0.这是几分钟后进入代码并将更改值输出到控制台，我发现在最后一步，当change = 0.01时，它会改变至0.009999999999999787。为什么会发生这种情况？

It should all work but at the last step when there's $0.01 leftover, number of pennies should be 1 but instead, it's 0. After a few minutes of stepping into the code and outputting the change value to the console, I've found out that at the last step when change = 0.01, it changes to 0.009999999999999787. Why is this happening?

推荐答案

使用 double 想法，为什么不使用Double或Float来代表货币？一>。我建议使用 BigDecimal 或每分钟计算一分钱。

Using double for currency is a bad idea, Why not use Double or Float to represent currency?. I recommend using BigDecimal or doing every calculation in cents.

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