C#减不准确，即使小数点? [英] c# Subtract is not accurate even with decimals?
问题描述
我正在学习TDD，因此决定创建一个Calculator类开始. 我首先做了基本的操作，现在我正在使用平方根函数.
I'm learning TDD and, decided to create a Calculator class to start. i did the basic first, and now I'm on the Square Root function.
我正在使用此方法获取根 http://www. math.com/school/subject1/lessons/S1U1L9DP.html 我用很少的数字对其进行了测试，而且我始终能获得准确的答案............................................................................................ 很容易理解.
I'm using this method to get the root http://www.math.com/school/subject1/lessons/S1U1L9DP.html i tested it with few numbers, and I always get the accurate answers. is pretty easy to understand.
现在我遇到了一个奇怪的问题，因为有了一些数字，我就得到了正确的答案，而有了一些数字，我就没有了.
Now I'm having a weird problem, because with some numbers, im getting the right answer, and with some, I don't.
我调试了代码，发现使用减法时没有得到正确的答案.
I debugged the code, and found out that I'm not getting the right answer when I use subtract.
我使用小数来获得最准确的结果.
I'm using decimals to get the most accurate result.
当我这样做:
18 / 4.25
我目前正在:4.2352941176470588235294117647
应为:4.2352941176470588235294117647059(使用Windows计算器)
when it should be: 4.2352941176470588235294117647059 (using windows calculator)
在这条路的尽头，这是我最接近18根的地方:
in the end of the road, this is the closest i get to the root of 18:
4.2426406871192851464050688705 ^ 2 = 18.000000000000000000000022892
我的问题是:
我能得到比这更准确的信息吗?
Can i get more accurate then this?
推荐答案
4.2352941176470588235294117647包含29位数字.
decimal 被定义为具有28-29个有效数字.您不能在decimal中存储更准确的数字.
decimal is define to have 28-29 significant digits. You can't store a more accurate number in a decimal.
您从事的工程或科学领域是第30位或更多位数对总体计算的准确性具有重要意义?
What field of engineering or science are you working in where the 30th and more digits are significant to the accuracy of the overall calculation?
(如果您显示了更多实际的代码，这也可能会有所帮助.您显示的唯一代码是18 / 4.25，它不能在您的代码中作为实际表达式，因为第二个数字是double文字，并且在没有强制转换的情况下不能将表达式的结果分配给decimal.
(It would also, possibly, help if you'd shown some more actual code. The only code you've shown is 18 / 4.25, which can't be an actual expression in your code, since the second number is a double literal, and you can't assign the result of this expression to a decimal without a cast).
如果需要任意精度，则没有标准的"BigRational"类型，但是有一个 BigInteger .如果需要，可以使用它来构造BigRational类型(将分子和分母存储为两个单独的整数).一个关于为什么还没有标准类型的猜测是关于何时的决定，例如规范此类理性可能会影响绩效或平等比较.
If you need arbitrary precision, then there isn't a standard "BigRational" type, but there is a BigInteger. You could use that to construct a BigRational type if you need that (storing numerator and denominator as two separate integers). One guess of why there isn't a standard type yet is that decisions on when to e.g. normalize such rationals may affect performance or equality comparisons.
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