数学运算和整数的浮点不准确性[重复]

Question

嘿，所以我正在尝试学习 Java，我知道浮点数不准确等等，但我现在感觉很盲目。我知道我做错了什么，电脑没有错，但我不知道在哪里。

我将数学返回值转换为整数，然后从变量 cash 中减去特定的整数值；当我从浮点数中减去整数时，浮点数似乎丢失了数据。我的问题如下：在不减慢程序速度的情况下避免数据损坏的最明智方法是什么？

<!-- language: lang-java -->
private static void calculateChange()
{
    System.out.print("Please enter any amount of cash in dollars: ");
    float cash = scanner.nextFloat();

    int ten_dollars = (int) Math.floor(cash/10);
    cash -= 10 * ten_dollars;

    System.out.println(cash);

    int five_dollars = (int) Math.floor(cash/5);
    cash -= 5 * five_dollars;
    int dollars = (int) Math.floor(cash);
    cash -= dollars;
    int quarters = (int) Math.floor(cash/0.25);
    cash -= 0.25 * quarters;
    int dimes = (int) Math.floor(cash/0.1);
    cash -= 0.1 * dimes;
    int nickels = (int) Math.floor(cash/0.05);
    cash -= 0.05 * nickels;
    int pennies = (int) Math.floor(cash/0.01);

    System.out.println("This is equal to:\n" + ten_dollars + " ten dollar bills\n"
            + five_dollars + " five dollar bills\n"
            + dollars + " one dollar bills\n"
            + quarters + " quarters\n"
            + dimes + " dimes\n"
            + nickels + " nickels\n"
            + pennies + " pennies");
}

运行：

请输入任意金额的美元现金：135,04

5.0399933

这等于：

13 十美元的钞票

一张五美元的钞票

0 一美元的钞票

0 个季度

0 角钱

0 镍

3 便士

构建成功（总时间：6 秒）

Answer 1

我认为您将所有内容乘以 100 并将您的美元金额表示为 int 表示便士的数量是正确的。但是，如果您首先使用 getFloat 输入浮点值，则需要在乘以 100 后使用 Math.round 对值进行四舍五入。

这行得通：

System.out.print("Please enter any amount of cash in dollars: ");
float cash = scanner.nextFloat();
int cashInPennies = Math.round(cash*100);
System.out.println(cashInPennies);
// If you say cashInPennies = (int)(cash*100), the result will be 13503 instead of
// 13504.

int ten_dollars = cashInPennies/1000;
cashInPennies %= 1000;

System.out.println(cashInPennies);

int five_dollars = cashInPennies/500;
cashInPennies %= 500;
int dollars = cashInPennies/100;
cashInPennies %= 100;
int quarters = cashInPennies/25;
cashInPennies %= 25;
int dimes = cashInPennies/10;
cashInPennies %= 10;
int nickels = cashInPennies/5;
cashInPennies %= 5;
int pennies = cashInPennies;
System.out.println("This is equal to:\n" + ten_dollars + " ten dollar bills\n"
        + five_dollars + " five dollar bills\n"
        + dollars + " one dollar bills\n"
        + quarters + " quarters\n"
        + dimes + " dimes\n"
        + nickels + " nickels\n"
        + pennies + " pennies");

Answer 2

你可以像这样使用BigDecimal，

// Pass the amount in
private static void calculateChange(BigDecimal cash) {
  BigDecimal TEN = new BigDecimal(10);
  BigDecimal FIVE = new BigDecimal(5);
  BigDecimal QUARTER = new BigDecimal("0.25");
  BigDecimal TENTH = new BigDecimal("0.1");
  BigDecimal FIVE100ths = new BigDecimal("0.05");

  int ten_dollars = cash.divide(TEN).intValue();
  cash = cash.subtract(TEN.multiply(new BigDecimal(ten_dollars)));

  System.out.println(cash);

  int five_dollars = cash.divide(FIVE).intValue();
  cash = cash.subtract(FIVE.multiply(new BigDecimal(five_dollars)));
  int dollars = cash.divide(BigDecimal.ONE).intValue();
  cash = cash.subtract(new BigDecimal(dollars));
  int quarters = cash.divide(QUARTER).intValue();
  cash = cash.subtract(QUARTER.multiply(new BigDecimal(quarters)));
  int dimes = cash.divide(TENTH).intValue();
  cash = cash.subtract(TENTH.multiply(new BigDecimal(dimes)));
  int nickels = cash.divide(FIVE100ths).intValue();
  cash = cash.subtract(FIVE100ths.multiply(new BigDecimal(nickels)));
  int pennies = cash.multiply(new BigDecimal(100)).intValue();

  System.out.println("This is equal to:\n"
      + ten_dollars + " ten dollar bills\n"
      + five_dollars + " five dollar bills\n"
      + dollars + " one dollar bills\n" + quarters
      + " quarters\n" + dimes + " dimes\n" + nickels
      + " nickels\n" + pennies + " pennies");
}