双或浮动数据类型不正确地在循环中引用？ [英] double or float datatype doesn't addup properly in a loop?

问题描述

在一个循环中，我加了0.10，直到达到所需的＃并获得索引。这是我的代码：

  private static int getIndexOfUnits（float units）{
 int index = -1; 
 float addup = 0.10f; 
 for（float i = 1.00f; i< units; i =（float）i + addup）{
 index ++; 
 System.out.println（I =+ i +Index =+ index）; 
} 
 
 return index; 
 
 
 
 $ b $ p 
 $ b如果通过的单位是5.7，我看到的输入是：
  I = 1.0指数= 0 
 I = 1.1指数= 1 
 I = 1.2指数= 2 
 I = 1.3000001指数= 3 
 I = 1.4000001指数= 4 
 I = 1.5000001指数= 5 
 I = 1.6000001指数= 6 
 I = 1.7000002指数= 7 
 I = 1.8000002指数= 8 
 I = 1.9000002指数= 9 
 I = 2.0000002指数= 10 
 I = 2.1000001指数= 11 
 I = 2.2指数= 12 
 I = 2.3指数= 13 
 I = 2.3999999指数= 14 
 I = 2.4999998指数= 15 
 I = 2.5999997指数= 16 
 I = 2.6999996指数= 17 
 I = 2.7999995指数= 18 
 I = 2.8999994指数= 19 
 I = 2.9999993指数= 20 
 I = 3.0999992指数= 21 
 I = 3.199999指数= 22 
 I = 3.299999 Index = 23 
 I = 3.399999 Index = 24 
 I = 3.4999988 Index = 25 
 I = 3.5999987 Index = 26 
 I = 3.6999986 Index = 27 
 I = 3.7999985指数= 28 
 I = 3.8999984指数= 29 
 I = 3.9999983指数= 30 
 I = 4.0999985指数= 31 
 I = 4.1999984指数= 32 
 I = 4.2999983指数= 33 
 I = 4.399998指数= 34 
 I = 4.499998指数= 35 
 I = 4.599998指数= 36 
 I = 4.699998指数= 37 
 I = 4.799998指数= 38 
 I = 4.8999977指数= 39 
 I = 4.9999976指数= 40 
 I = 5.0999975指数= 41 
 I = 5.1999974指数= 42 
 I = 5.2999973指数= 43 
 I = 5.399997指数= 44 
 I = 5.499997指数= 45 
 I = 5.599997 Index = 46 
 I = 5.699997 Index = 47 
  
单位是18.90或29.90这样的大数字，给出了错误的指标。索引通常比应该少1。最初只添加0.10，但在2.3之后，它得到2.39999 ....添加0.10。我相信这是一个精确的问题。如何处理它，并确保我得到正确的大＃的指数也无论使用浮动或双。 
 
 
 
任何想法!!!!  
解决方案
 href =http://floating-point-gui.de/basic/ =noreferrer>浮点指南： 
 
 
 
 
 为什么我的数字，比如0.1 + 0.2加起来不错0.3回合，而
取而代之，我得到了一个奇怪的结果，比如0.30000000000000004？ 
 
 
 
因为在内部，计算机使用的格式（二进制浮点）
不能准确地表示一个数字，如0.1,0.2或0.3。
 
 
在编译或解释代码时，您的0.1已经是
，以该格式四舍五入到最接近的数字，甚至在计算发生之前会导致小的
舍入误差。
 
您不使用 float 或 double 如果你需要数字来合计exaclty。改用 BigDecimal 。
 
In a loop I am adding 0.10 till I reach the desired #, and getting the index. This is my code :
    private static int getIndexOfUnits(float units) {
    int index = -1;
    float addup = 0.10f;
    for(float i = 1.00f; i < units; i=(float)i+addup) {
        index++;
        System.out.println("I = " + i + " Index = " + index);
    }

    return index;
}
If the units passed is 5.7, the ourput I see is :
I = 1.0 Index = 0
I = 1.1 Index = 1
I = 1.2 Index = 2
I = 1.3000001 Index = 3
I = 1.4000001 Index = 4
I = 1.5000001 Index = 5
I = 1.6000001 Index = 6
I = 1.7000002 Index = 7
I = 1.8000002 Index = 8
I = 1.9000002 Index = 9
I = 2.0000002 Index = 10
I = 2.1000001 Index = 11
I = 2.2 Index = 12
I = 2.3 Index = 13
I = 2.3999999 Index = 14
I = 2.4999998 Index = 15
I = 2.5999997 Index = 16
I = 2.6999996 Index = 17
I = 2.7999995 Index = 18
I = 2.8999994 Index = 19
I = 2.9999993 Index = 20
I = 3.0999992 Index = 21
I = 3.199999 Index = 22
I = 3.299999 Index = 23
I = 3.399999 Index = 24
I = 3.4999988 Index = 25
I = 3.5999987 Index = 26
I = 3.6999986 Index = 27
I = 3.7999985 Index = 28
I = 3.8999984 Index = 29
I = 3.9999983 Index = 30
I = 4.0999985 Index = 31
I = 4.1999984 Index = 32
I = 4.2999983 Index = 33
I = 4.399998 Index = 34
I = 4.499998 Index = 35
I = 4.599998 Index = 36
I = 4.699998 Index = 37
I = 4.799998 Index = 38
I = 4.8999977 Index = 39
I = 4.9999976 Index = 40
I = 5.0999975 Index = 41
I = 5.1999974 Index = 42
I = 5.2999973 Index = 43
I = 5.399997 Index = 44
I = 5.499997 Index = 45
I = 5.599997 Index = 46
I = 5.699997 Index = 47
If the units is big number like 18.90 or 29.90, it gives wrong index. Index is normally 1 less then it should be. Initial only 0.10 was added but after 2.3, it gets 2.39999.... on adding 0.10 to it. I believe this is a matter of precision. How to handle it and make sure that I get the right index on big #'s also regardless of using float or double. 

Any ideas !!!!
解决方案
From the Floating-Point Guide:

  
Why don’t my numbers, like 0.1 + 0.2 add up to a nice round 0.3, and
  instead I get a weird result like 0.30000000000000004?
  
  
Because internally, computers use a format (binary floating-point)
  that cannot accurately represent a number like 0.1, 0.2 or 0.3 at all.
  
  
When the code is compiled or interpreted, your "0.1" is already
  rounded to the nearest number in that format, which results in a small
  rounding error even before the calculation happens.
You cnnot use float or double if you need numbers to add up exaclty. Use BigDecimal instead.

                        
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