blocks|key|5973874|text|使用decimal而不是double，一切都会好起来：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5973875|decimal+Num+=+6578336356630531.0m;
string+StringNum+=+Num.ToString("000.0");|code-block|syntax|javascript|5973876|这个问题与双值表示和精度有关。|5973877|entityMap^0|2|7|C|6|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Use <code>decimal</code> instead of <code>double</code> and everything will be OK:

<pre><code>decimal Num = 6578336356630531.0m;
string StringNum = Num.ToString("000.0");
</code></pre>

The problem is connected with double values representation and precision.

blocks|key|2621507|text|double不能存储该精确度。如果这是你想要的行为，就使用decimal。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2621508|entityMap^0|0|6|T|7|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>double</code> cannot store that amount of precision. Use a <code>decimal</code> if that's the behaviour you want.

blocks|key|5973989|text|问题是您存储的值恰好是6578336356630531。没有更接近6578336356630530的double值。因此，对于执行时存在的数据，输出是正确的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5973990|来自the+documentation|5973991|5973992|所有浮点数的有效位数也是有限的，这也决定了浮点值近似实数的精确度。双精度值的精度最多为15位小数，但内部最多保留17位。|blockquote|5973993|5973994|5973995|你在吹毛求疵地说第16位数字。|5973996|我有一个handy+class，它可以让你看到任何double的确切值。|5973997|如果您需要更高的精度，请使用decimal而不是double。请注意，decimal的范围较小，但精度较高。|5973998|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.double.aspx|1|http://yoda.arachsys.com/csharp/DoubleConverter.cs^0|B|G|1E|6|0|2|H|0|0|0|0|0|0|0|P|6|4|B|1|0|E|7|O|6|Z|7|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|H|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|1D|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1G|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@$9|1K|A|1L|1|1M]]|E|$]]|$1|R|3|S|5|6|7|1N|8|@$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1U|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]|11|$5|W|X|Y|E|$Z|12]]]]

The trouble is the value you're storing is exactly <code>6578336356630531</code>. There is no <code>double</code> value closer to 6578336356630530. So the output is correct for the data present at execution time.

From <a href="http://msdn.microsoft.com/en-us/library/system.double.aspx" rel="nofollow">the documentation</a>:

<blockquote>
 All floating-point numbers also have a limited number of significant digits, which also determines how accurately a floating-point value approximates a real number. A Double value has up to 15 decimal digits of precision, although a maximum of 17 digits is maintained internally. 
</blockquote>

You're quibbling about the 16th digit.

I have a <a href="http://yoda.arachsys.com/csharp/DoubleConverter.cs" rel="nofollow">handy class</a> which lets you see the exact value of any <code>double</code>.

If you need more precision than that, use <code>decimal</code> instead of <code>double</code>. Note that <code>decimal</code> has a smaller range but higher precision.

blocks|key|5974032|text|看起来你找到了一个浮点数无法正确表示的数字。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5974033|请尝试使用小数：|5974034|decimal+Num+=+6578336356630531.0m;
string+StringNum+=+Num.ToString("###.0");|code-block|syntax|javascript|5974035|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

It would seem you have found a number that cannot be represented by a floating-point numkber correctly.

try using a decimal instead:

<pre><code>decimal Num = 6578336356630531.0m;
string StringNum = Num.ToString("###.0");
</code></pre>

blocks|key|497227|text|你会用小数点吗？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|497228|decimal+Num+=+6578336356630531.0M;
string+StringNum+=+Num+.ToString("000.0");|code-block|syntax|javascript|497229|double是一个近似精度的浮点型。See+here.|offset|length|style|CODE|497230|文章摘录：|497231|497232|浮点值和精度损失|blockquote|497233|497234|请记住，浮点数只能近似十进制数，并且浮点数的精度决定了该数字近似十进制数的精度。默认情况下，双精度值包含15位小数精度，但内部最多保留17位。浮点数的精度有几个结果:在特定精度下看起来相等的两个浮点数可能不相等，因为它们的最低有效位不同。如果使用十进制数，则使用浮点数的数学或比较运算可能不会产生相同的结果，因为浮点数可能不完全接近十进制数。如果涉及浮点数，则值可能不会往返。如果操作将原始浮点数转换为另一种形式，反向操作将转换后的形式转换回浮点数，并且最终的浮点数等于原始浮点数，则称该值为往返。往返可能会失败，因为一个或多个最低有效数字在转换过程中丢失或更改。|497235|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.double%2528v=vs.90%2529.aspx^0|0|0|0|6|I|9|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|15|8|@$I|16|J|17|K|L]]|9|@$I|18|J|19|1|1A]]|A|$]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1D|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|1F|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|W|$X|$5|Y|Z|10|A|$11|12]]]]

Can you use a decimal?
<pre><code>decimal Num = 6578336356630531.0M;
string StringNum = Num .ToString(&quot;000.0&quot;);
</code></pre>
<code>double</code> is a float which approximates precision. <a href="http://msdn.microsoft.com/en-us/library/system.double%28v=vs.90%29.aspx" rel="nofollow noreferrer">See here.</a>
Article excerpt:
<blockquote>
Floating-Point Values and Loss of Precision
Remember that a
floating-point number can only approximate a decimal number, and that
the precision of a floating-point number determines how accurately
that number approximates a decimal number. By default, a Double value
contains 15 decimal digits of precision, although a maximum of 17
digits is maintained internally. The precision of a floating-point
number has several consequences: Two floating-point numbers that
appear equal for a particular precision might not compare equal
because their least significant digits are different. A mathematical
or comparison operation that uses a floating-point number might not
yield the same result if a decimal number is used because the
floating-point number might not exactly approximate the decimal
number. A value might not roundtrip if a floating-point number is
involved. A value is said to roundtrip if an operation converts an
original floating-point number to another form, an inverse operation
transforms the converted form back to a floating-point number, and the
final floating-point number is equal to the original floating-point
number. The roundtrip might fail because one or more least significant
digits are lost or changed in a conversion.
</blockquote>

blocks|key|5974156|text|不进行双精度舍入的最大整数是2%5E53+-+1，大约是9e15，但是你有6e15，它可能被精确地表示，但不一定。你的运气不好(经常是那种坏运气；处理它)。如果你想生活在没有这些惊喜的情况下，你必须在c#中使用decimal类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5974157|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Maximal whole number without rounding in double precision is 2^53 - 1, which is approx 9e15, but you have 6e15, which may possibly be represented preciously, but not necessarily. You had a bad luck (quite often type of bad luck; deal with it). If you want to live without these surprises, you have to use decimal type in c#.

In my c# console application, I want to convert double variable to string type. but resultant string variable should have at least 3 digit to left of decimal point and one digit to right of it.
example: 3.4569 should converted to "003.4"

It works for above example, but throws wrong result for following conversion.

<pre><code> double Num = Math.Pow((3 + Math.Sqrt(5)), N); //6578336356630531.0 for N=22
 string StringNum = Num .ToString("000.0");
</code></pre>

It results..

<pre><code> StringNum ="6578336356630530.0";
</code></pre>

but it would be..

<pre><code> StringNum ="6578336356630531.0";
</code></pre>

How do i get exact string value for these type of numbers??

<pre><code> //decimal Num=Convert.ToDecimal (Math.Pow((3 + Math.Sqrt(5)), N));
 //this conversion also looses original value
</code></pre>

Thanx..

tostring("000.0") generating wrong value

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在我的c#控制台应用程序中，我希望将双精度变量转换为字符串类型。但是结果字符串变量应该至少有小数点左边的3位和小数点右边的1位。示例: 3.4569应转换为"003.4“它对上面的例子有效，但对于后面的转换抛出错误的结果。 double Num = Math.Pow((3 + Math.Sqrt(5)), N); //...

问tostring("000.0")生成错误的值
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问tostring("000.0")生成错误的值EN