循环中显示0的问题。 [英] Problem with display 0 in loop.

问题描述

你好，



我试图创建简单的while循环，直到我的变量为0.

所以创建了一个

 做 
 {
x = x +  0 。 001 ; 
 cout<< x0<< ENDL; 
}  while （ SOME_CALCULATION ！=  0 ）; 

一切正常，直到我的循环达到0然后我得到7.63278e-017而不是0.



循环示例：

< br /> 
结果：-0.003< br /> 
结果：-0.002< br /> 
结果：-0.001< br /> 
结果：7.63278e-017< br /> 
结果：0.001< br / > 
结果：0.002< br /> 
结果：0.003< br /> 

解决方案

你应该只知道浮点类型不代表实数（实数中，数字通常代表无限量的信息;这是无法在计算机中的有限状态机中表示的东西:-)）;它们代表了一些近似。



我记得，在Donald E. Knuth最着名的书中， The Art计算机编程，Knuth警告读者不要在浮点类型上使用相等比较（'=='，在C / C ++ / C＃术语中）。相反，您可以使用 fabs（value1 - value2）< someSmallNumber; 其中 someSmallNumber 由特定问题定义， fabs 是：

http://www.cplusplus.com/reference/cmath/fabs [< a href =http://www.cplusplus.com/reference/cmath/fabstarget =_ blanktitle =New Window> ^ ]。



在你的情况下，它是而（fabs（SOME_CALCULATION）< someSmallNumber）。



请参阅：

http://en.wikipedia.org/wiki/The_Art_of_Computer_Programming [ ^ ]，

http://en.wikipedia.org/wiki/Donald_Knuth [ ^ ]。

-SA

Hello,

Am trying to create simple while loop until my variable will be 0.
So am created a

do
{
x = x + 0.001;
cout << x0 << endl;
} while (SOME_CALCULATION != 0);

Everything works great until my loop reach 0 then i getting 7.63278e-017 instead of 0.

Loop example:

<br />
result: -0.003<br />
result: -0.002<br />
result: -0.001<br />
result: 7.63278e-017<br />
result: 0.001<br />
result: 0.002<br />
result: 0.003<br />

解决方案

You should just understand that floating-point types do not represent real numbers (in real numbers, a number generally represents infinite amount of information; this is something which cannot be represented in a finite-state machine like a computer :-)); they represent some approximation.

As I remember, in the most well-known book by Donald E. Knuth, The Art of Computer Programming, Knuth warned the readers against using equality comparison ('==', in C/C++/C# terms) on floating-point types. Instead, you can use fabs(value1 - value2) < someSmallNumber; where someSmallNumber is defined by a particular problem, and fabs is this:
http://www.cplusplus.com/reference/cmath/fabs[^].

In your case, it would be while (fabs(SOME_CALCULATION) < someSmallNumber).

Please see also:
http://en.wikipedia.org/wiki/The_Art_of_Computer_Programming[^],
http://en.wikipedia.org/wiki/Donald_Knuth[^].

—SA

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