blocks|key|1671551|text|对于任何在Silverlight上使用C#进行开发的人来说，这里有一个我刚刚发现的非常巧妙的技巧，它允许通过调用Javascript引擎来计算表达式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1671552|double+result+=+(double)+HtmlPage.Window.Eval("15+%2B+35");|code-block|syntax|javascript|1671553|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For anybody developing in C# on Silverlight here's a pretty neat trick that I've just discovered that allows evaluation of an expression by calling out to the Javascript engine:

<pre><code>double result = (double) HtmlPage.Window.Eval("15 + 35");
</code></pre>

blocks|key|1671578|text|实际上，有一种内置的方法--你可以使用XPath命名空间！尽管它要求您重新格式化字符串以使用XPath表示法进行确认。我曾经使用过这样的方法来处理简单的表达式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1671579|++++public+static+double+Evaluate(string+expression)
++++{
++++++++var+xsltExpression+=+
++++++++++++string.Format("number({0})",+
++++++++++++++++new+Regex(@"([\%2B\-\*])").Replace(expression,+"+${1}+")
++++++++++++++++++++++++++++++++++++++++.Replace("/",+"+div+")
++++++++++++++++++++++++++++++++++++++++.Replace("%25",+"+mod+"));

++++++++return+(double)new+XPathDocument
++++++++++++(new+StringReader("<r/>"))
++++++++++++++++.CreateNavigator()
++++++++++++++++.Evaluate(xsltExpression);
++++}|code-block|syntax|javascript|1671580|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Actually there is kind of a built in one - you can use the XPath namespace!
Although it requires that you reformat the string to confirm with XPath notation. I've used a method like this to handle simple expressions:

<pre><code> public static double Evaluate(string expression)
 {
 var xsltExpression = 
 string.Format("number({0})", 
 new Regex(@"([\+\-\*])").Replace(expression, " ${1} ")
 .Replace("/", " div ")
 .Replace("%", " mod "));

 return (double)new XPathDocument
 (new StringReader("&lt;r/&gt;"))
 .CreateNavigator()
 .Evaluate(xsltExpression);
 }
</code></pre>

blocks|key|1456684|text|你看到http://ncalc.codeplex.com了吗？|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1456685|它的可扩展性，快速(例如，有自己的缓存)使你能够通过处理EvaluateFunction/EvaluateParameter事件在运行时提供自定义函数和变量。它可以解析的示例表达式：|1456686|Expression+e+=+new+Expression("Round(Pow(Pi,+2)+%2B+Pow([Pi2],+2)+%2B+X,+2)");+

++e.Parameters["Pi2"]+=+new+Expression("Pi+*+Pi");+
++e.Parameters["X"]+=+10;+

++e.EvaluateParameter+%2B=+delegate(string+name,+ParameterArgs+args)+
++++{+
++++++if+(name+==+"Pi")+
++++++args.Result+=+3.14;+
++++};+

++Debug.Assert(117.07+==+e.Evaluate());+|code-block|syntax|javascript|1456687|它还在本地处理unicode+&许多数据类型。如果你想改变语法，它会附带一个鹿角文件。还有一个fork，它支持MEF加载新函数。|1456688|entityMap|0|LINK|mutability|MUTABLE|url|http://ncalc.codeplex.com/^0|3|P|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Have you seen <a href="http://ncalc.codeplex.com" rel="noreferrer">http://ncalc.codeplex.com</a> ? 

It's extensible, fast (e.g. has its own cache) enables you to provide custom functions and varaibles at run time by handling EvaluateFunction/EvaluateParameter events. Example expressions it can parse: 

<pre><code>Expression e = new Expression("Round(Pow(Pi, 2) + Pow([Pi2], 2) + X, 2)"); 

 e.Parameters["Pi2"] = new Expression("Pi * Pi"); 
 e.Parameters["X"] = 10; 

 e.EvaluateParameter += delegate(string name, ParameterArgs args) 
 { 
 if (name == "Pi") 
 args.Result = 3.14; 
 }; 

 Debug.Assert(117.07 == e.Evaluate()); 
</code></pre>

It also handles unicode &amp; many data type natively. It comes with an antler file if you want to change the grammer. There is also a fork which supports MEF to load new functions.

blocks|key|1671719|text|如果你需要非常简单的东西，你可以使用DataTable+:-)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1671720|Dim+dt+As+New+DataTable
dt.Columns.Add("A",+GetType(Integer))
dt.Columns.Add("B",+GetType(Integer))
dt.Columns.Add("C",+GetType(Integer))
dt.Rows.Add(New+Object()+{12,+13,+DBNull.Value})

Dim+boolResult+As+Boolean+=+dt.Select("A>B-2").Length+>+0

dt.Columns.Add("result",+GetType(Integer),+"A%2BB*2%2BISNULL(C,0)")
Dim+valResult+As+Object+=+dt.Rows(0)("result")|code-block|syntax|javascript|1671721|entityMap^0|I|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

If you need very simple thing you can use the <code>DataTable</code> :-)

<pre class="lang-vb prettyprint-override"><code>Dim dt As New DataTable
dt.Columns.Add("A", GetType(Integer))
dt.Columns.Add("B", GetType(Integer))
dt.Columns.Add("C", GetType(Integer))
dt.Rows.Add(New Object() {12, 13, DBNull.Value})

Dim boolResult As Boolean = dt.Select("A&gt;B-2").Length &gt; 0

dt.Columns.Add("result", GetType(Integer), "A+B*2+ISNULL(C,0)")
Dim valResult As Object = dt.Rows(0)("result")
</code></pre>

blocks|key|1671740|text|namespace+CalcExp
{
++++internal+class+Program
++++{
++++++++private+static+void+Main(string[]+args)
++++++++{
++++++++++++double+res+=+Evaluate("4%2B5/2-1");

++++++++++++Console.WriteLine(res);

++++++++}

++++++++public+static+double+Evaluate(string+expression)
++++++++{
++++++++++++var+xsltExpression+=
++++++++++++++++string.Format("number({0})",
++++++++++++++++++++new+Regex(@"([\%2B\-\*])").Replace(expression,+"+${1}+")
++++++++++++++++++++++++++++++++++++++++++++.Replace("/",+"+div+")
++++++++++++++++++++++++++++++++++++++++++++.Replace("%25",+"+mod+"));

//+ReSharper+disable+PossibleNullReferenceException
++++++++++++return+(double)new+XPathDocument
++++++++++++++++(new+StringReader("<r/>"))
++++++++++++++++++++.CreateNavigator()
++++++++++++++++++++.Evaluate(xsltExpression);
//+ReSharper+restore+PossibleNullReferenceException
++++++++}

++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1671741|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>namespace CalcExp
{
 internal class Program
 {
 private static void Main(string[] args)
 {
 double res = Evaluate("4+5/2-1");

 Console.WriteLine(res);

 }

 public static double Evaluate(string expression)
 {
 var xsltExpression =
 string.Format("number({0})",
 new Regex(@"([\+\-\*])").Replace(expression, " ${1} ")
 .Replace("/", " div ")
 .Replace("%", " mod "));

// ReSharper disable PossibleNullReferenceException
 return (double)new XPathDocument
 (new StringReader("&lt;r/&gt;"))
 .CreateNavigator()
 .Evaluate(xsltExpression);
// ReSharper restore PossibleNullReferenceException
 }

 }
}
</code></pre>

blocks|key|1456831|text|我也会看看杰斯(https://github.com/pieterderycke/Jace)。.NET是一个高性能的数学解析器和计算引擎，支持所有的Jace风格(Jace+4.x，Windows+Phone，Windows+Store，...)。Jace也可以通过NuGet获得：https://www.nuget.org/packages/Jace|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1456832|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/pieterderycke/Jace|1|https://www.nuget.org/packages/Jace^0|8|11|0|3W|Z|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

I would also have a look at Jace (<a href="https://github.com/pieterderycke/Jace" rel="nofollow">https://github.com/pieterderycke/Jace</a>). Jace is a high performance math parser and calculation engine that supports all the .NET flavors (.NET 4.x, Windows Phone, Windows Store, ...). Jace is also available through NuGet: <a href="https://www.nuget.org/packages/Jace" rel="nofollow">https://www.nuget.org/packages/Jace</a>

blocks|key|1456891|text|最初，我对muparser使用c#包装器。这是非常快的。我所知道的唯一更快的解决方案是exprtk。如果您正在寻找其他解决方案，可以查看benchmark。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1456892|但是在使用.Net的情况下，您可以使用内置支持在运行时编译代码。这个想法是有一个“模板”源文件作为嵌入式资源，您可以在其中替换用于评估的公式。然后将准备好的class-source-code传递给编译器。|1456893|基本模板可能如下所示：|1456894|public+class+CSCodeEvaler
{
++++public+double+EvalCode()
++++{
++++++++return+last+=+Convert.ToDouble(%25formula%25);
++++}

++++public+double+last+=+0;
++++public+const+double+pi+=+Math.PI;
++++public+const+double+e+=+Math.E;
++++public+double+sin(double+value)+{+return+Math.Sin(value);+}
++++public+double+cos(double+value)+{+return+Math.Cos(value);+}
++++public+double+tan(double+value)+{+return+Math.Tan(value);+}
++++...|code-block|syntax|javascript|1456895|请注意将放入表达式的%25formula%25。|1456896|要进行编译，请使用类CSharpCodeProvider。我不想在这里放入完整的源代码。但this+answer可能会有所帮助：|1456897|加载内存中的程序集后，可以创建类的实例并调用EvalCode。|1456898|entityMap|0|LINK|mutability|MUTABLE|url|http://muparser.beltoforion.de/|1|http://www.partow.net/programming/exprtk/index.html|2|https://github.com/ArashPartow/math-parser-benchmark-project|3|https://stackoverflow.com/questions/3188882/compile-and-run-dynamic-code-without-generating-exe^0|5|8|0|17|6|1|1W|9|2|0|0|0|0|0|19|B|3|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@$A|17|B|18|1|19]|$A|1A|B|1B|1|1C]|$A|1D|B|1E|1|1F]]|C|$]]|$1|D|3|E|5|6|7|1G|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1H|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|1I|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|1J|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1K|8|@]|9|@$A|1L|B|1M|1|1N]]|C|$]]|$1|Q|3|R|5|6|7|1O|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1P|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]|12|$5|V|W|X|C|$Y|13]]|14|$5|V|W|X|C|$Y|15]]]]

Initially I used the c# wrapper for <a href="http://muparser.beltoforion.de/" rel="nofollow noreferrer">muparser</a>. This was very fast. The only faster solution I know is <a href="http://www.partow.net/programming/exprtk/index.html" rel="nofollow noreferrer">exprtk</a>. If you are looking for other solutions you can checkout the <a href="https://github.com/ArashPartow/math-parser-benchmark-project" rel="nofollow noreferrer">benchmark</a>.

But in case of .Net you can use the builtin support to compile code at runtime. The idea is to have a "template" source file as e.g. embedded resource where you can replace the formula for the evaluation. Then you pass this prepared class-source-code to the compiler.

A basic template could look like this:

<pre><code>public class CSCodeEvaler
{
 public double EvalCode()
 {
 return last = Convert.ToDouble(%formula%);
 }

 public double last = 0;
 public const double pi = Math.PI;
 public const double e = Math.E;
 public double sin(double value) { return Math.Sin(value); }
 public double cos(double value) { return Math.Cos(value); }
 public double tan(double value) { return Math.Tan(value); }
 ...
</code></pre>

Notice the %formula% where the expression will be put in.

To compile use the class CSharpCodeProvider. I do not want to put in the complete source here. But <a href="https://stackoverflow.com/questions/3188882/compile-and-run-dynamic-code-without-generating-exe">this answer</a> might help:

After you have the in memory assembly loaded you can create an instance of your class and call EvalCode.

blocks|key|1671981|text|最近我在使用mXparser，这是一个用于.NET和JAVA的数学解析库。mXparser支持基本公式以及非常花哨/复杂的公式(包括变量、函数、运算符、迭代和递归)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1671982|https://mxparser.codeplex.com/|offset|length|1671983|https://mathparser.org/|1671984|下面是几个使用示例：|1671985|示例1：|1671986|Expression+e+=+new+Expression("1%2B2*7+%2B+(sin(10)+-+2)/3");
double+v+=+e.calculate();|code-block|syntax|javascript|1671987|示例2：|1671988|Argument+x+=+new+Argument("x+=+5");
Expression+e+=+new+Expression("2*x%2B3",+x);
double+v+=+e.calculate();|1671989|示例3：|1671990|Function+f+=+new+Function("f(x,y)+=+sin(x)+/+cos(y)");
Expression+e+=+new+Expression("f(pi,+2*pi)+-+2",+f);
double+v+=+e.calculate();|1671991|最近发现-如果您想尝试语法(并查看高级用例)，您可以下载由mXparser提供支持的Scalar+Calculator+app。|1671992|诚挚的问候|1671993|entityMap|0|LINK|mutability|MUTABLE|url|1|2|https://scalarmath.org/|3|https://play.google.com/store/apps/details?id=org.mathparser.scalar.lite|4|https://play.google.com/store/apps/details?id=org.mathparser.scalar.pro^0|0|0|U|0|0|0|N|1|0|0|0|0|0|0|0|0|16|6|2|1D|A|3|1O|3|4|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1H|8|@]|9|@$D|1I|E|1J|1|1K]]|A|$]]|$1|F|3|G|5|6|7|1L|8|@]|9|@$D|1M|E|1N|1|1O]]|A|$]]|$1|H|3|I|5|6|7|1P|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|1R|8|@]|9|@]|A|$O|P]]|$1|Q|3|R|5|6|7|1S|8|@]|9|@]|A|$]]|$1|S|3|T|5|N|7|1T|8|@]|9|@]|A|$O|P]]|$1|U|3|V|5|6|7|1U|8|@]|9|@]|A|$]]|$1|W|3|X|5|N|7|1V|8|@]|9|@]|A|$O|P]]|$1|Y|3|Z|5|6|7|1W|8|@]|9|@$D|1X|E|1Y|1|1Z]|$D|20|E|21|1|22]|$D|23|E|24|1|25]]|A|$]]|$1|10|3|11|5|6|7|26|8|@]|9|@]|A|$]]|$1|12|3|-4|5|6|7|27|8|@]|9|@]|A|$]]]|13|$14|$5|15|16|17|A|$18|C]]|19|$5|15|16|17|A|$18|G]]|1A|$5|15|16|17|A|$18|1B]]|1C|$5|15|16|17|A|$18|1D]]|1E|$5|15|16|17|A|$18|1F]]]]

Recently I was using mXparser, which is a math parser library for .NET and JAVA. mXparser supports basic formulas as well as very fancy / complicated ones (including variables, functions, operators, iteration and recursion).

<a href="https://mxparser.codeplex.com/" rel="nofollow noreferrer">https://mxparser.codeplex.com/</a>

<a href="https://mathparser.org/" rel="nofollow noreferrer">https://mathparser.org/</a>

A few usage examples:

Example 1:

<pre><code>Expression e = new Expression("1+2*7 + (sin(10) - 2)/3");
double v = e.calculate();
</code></pre>

Example 2:

<pre><code>Argument x = new Argument("x = 5");
Expression e = new Expression("2*x+3", x);
double v = e.calculate();
</code></pre>

Example 3:

<pre><code>Function f = new Function("f(x,y) = sin(x) / cos(y)");
Expression e = new Expression("f(pi, 2*pi) - 2", f);
double v = e.calculate();
</code></pre>

Found recently - in case you would like to try the syntax (and see the advanced use case) you can download the <a href="https://scalarmath.org" rel="nofollow noreferrer">Scalar</a> <a href="https://play.google.com/store/apps/details?id=org.mathparser.scalar.lite" rel="nofollow noreferrer">Calculator</a> <a href="https://play.google.com/store/apps/details?id=org.mathparser.scalar.pro" rel="nofollow noreferrer">app</a> that is powered by mXparser.

Best regards

blocks|key|1457044|text|现在有了Roslyn，又有了另一个选择：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457045|您可以使用CodeAnalysis.CSharp.Scripting库来实现此目的。|1457046|using+Microsoft.CodeAnalysis.CSharp.Scripting;
using+System;

namespace+ExpressionParser
{
++++class+Program
++++{
++++++++static+void+Main(string[]+args)
++++++++{
++++++++++++//Demonstrate+evaluating+C#+code
++++++++++++var+result+=+CSharpScript.EvaluateAsync("System.DateTime.Now.AddDays(-1)+>+System.DateTime.Now").Result;
++++++++++++Console.WriteLine(result.ToString());

++++++++++++//Demonstrate+evaluating+simple+expressions
++++++++++++var+result2+=+CSharpScript.EvaluateAsync("+5+*+7").Result;
++++++++++++Console.WriteLine(result2);
++++++++++++Console.ReadKey();
++++++++}
++++}
}|code-block|syntax|javascript|1457047|nuget包：|1457048|<package+id="Microsoft.CodeAnalysis.Analyzers"+version="1.1.0"+targetFramework="net461"+/>
<package+id="Microsoft.CodeAnalysis.Common"+version="1.1.1"+targetFramework="net461"+/>
<package+id="Microsoft.CodeAnalysis.CSharp"+version="1.1.1"+targetFramework="net461"+/>
<package+id="Microsoft.CodeAnalysis.CSharp.Scripting"+version="1.1.1"+targetFramework="net461"+/>
<package+id="Microsoft.CodeAnalysis.Scripting"+version="1.1.1"+targetFramework="net461"+/>
<package+id="Microsoft.CodeAnalysis.Scripting.Common"+version="1.1.1"+targetFramework="net461"+/>|1457049|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Yet another option now that Roslyn is available:

You can use CodeAnalysis.CSharp.Scripting library for this.

<pre><code>using Microsoft.CodeAnalysis.CSharp.Scripting;
using System;

namespace ExpressionParser
{
 class Program
 {
 static void Main(string[] args)
 {
 //Demonstrate evaluating C# code
 var result = CSharpScript.EvaluateAsync("System.DateTime.Now.AddDays(-1) &gt; System.DateTime.Now").Result;
 Console.WriteLine(result.ToString());

 //Demonstrate evaluating simple expressions
 var result2 = CSharpScript.EvaluateAsync(" 5 * 7").Result;
 Console.WriteLine(result2);
 Console.ReadKey();
 }
 }
}
</code></pre>

nuget packages:

<pre><code>&lt;package id="Microsoft.CodeAnalysis.Analyzers" version="1.1.0" targetFramework="net461" /&gt;
&lt;package id="Microsoft.CodeAnalysis.Common" version="1.1.1" targetFramework="net461" /&gt;
&lt;package id="Microsoft.CodeAnalysis.CSharp" version="1.1.1" targetFramework="net461" /&gt;
&lt;package id="Microsoft.CodeAnalysis.CSharp.Scripting" version="1.1.1" targetFramework="net461" /&gt;
&lt;package id="Microsoft.CodeAnalysis.Scripting" version="1.1.1" targetFramework="net461" /&gt;
&lt;package id="Microsoft.CodeAnalysis.Scripting.Common" version="1.1.1" targetFramework="net461" /&gt;
</code></pre>

blocks|key|1457111|text|一个简单的数学解析器很容易构建，并且只需要几行代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457112|以这个灵活的例子为例：|1457113|class+RPN
{
++++public+static+double+Parse(+Stack<string>+strStk+)
++++{
++++++++if+(strStk+==+null+%7C%7C+strStk.Count+==+0+)
++++++++{
++++++++++++return+0;
++++++++}
++++++++Stack<double>+numStk+=+new+Stack<double>();
++++++++double+result+=+0;

++++++++Func<double,+double>+op+=+null;
++++++++while+(strStk.Count+>+0)
++++++++{
++++++++++++var+s+=+strStk.Pop();
++++++++++++switch+(s)
++++++++++++{
++++++++++++++++case+"%2B":
++++++++++++++++++++op+=+(+b+)+=>+{+return+numStk.Pop()+%2B+b;+};
++++++++++++++++++++break;
++++++++++++++++case+"-":
++++++++++++++++++++op+=+(+b+)+=>+{+return+numStk.Pop()+-+b;+};
++++++++++++++++++++break;
++++++++++++++++case+"*":
++++++++++++++++++++op+=+(+b+)+=>+{+return+numStk.Pop()+*+b;+};
++++++++++++++++++++break;
++++++++++++++++case+"/":
++++++++++++++++++++op+=+(+b+)+=>+{+return+numStk.Pop()+/+b;+};
++++++++++++++++++++break;

++++++++++++++++default:
++++++++++++++++++++double.TryParse(s,+NumberStyles.Any,+out+result);
++++++++++++++++++++if+(numStk.Count+>+0)
++++++++++++++++++++{
++++++++++++++++++++++++result+=+op(result);
++++++++++++++++++++}
++++++++++++++++++++numStk.Push(result);
++++++++++++++++++++break;
++++++++++++}
++++++++}
++++++++return+result;
++++}
}

....
var+str+=+"+100.5+%2B+300.5+-+100+*+10+/+100";++++
str+=+Regex.Replace(str,+@"\s",+"",+RegexOptions.Multiline);
Stack<string>+strStk+=+new+Stack<string>(
+++++Regex.Split(str,+@"([()*%2B\/-])",+RegexOptions.Multiline).Reverse()
);
RPN.Parse(strStk);|code-block|syntax|javascript|1457114|通过包围堆栈来启用优先级就足够了，例如通过递归归档。括号之间的任何内容都放在一个新的堆栈上。最后，您可以通过lambdas以一种干净、可读的方式支持数学运算。|1457115|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

A simple math parser is quite easy to build, and requires only a few lines of code:

Take this flexible example:

<pre><code>class RPN
{
 public static double Parse( Stack&lt;string&gt; strStk )
 {
 if (strStk == null || strStk.Count == 0 )
 {
 return 0;
 }
 Stack&lt;double&gt; numStk = new Stack&lt;double&gt;();
 double result = 0;

 Func&lt;double, double&gt; op = null;
 while (strStk.Count &gt; 0)
 {
 var s = strStk.Pop();
 switch (s)
 {
 case "+":
 op = ( b ) =&gt; { return numStk.Pop() + b; };
 break;
 case "-":
 op = ( b ) =&gt; { return numStk.Pop() - b; };
 break;
 case "*":
 op = ( b ) =&gt; { return numStk.Pop() * b; };
 break;
 case "/":
 op = ( b ) =&gt; { return numStk.Pop() / b; };
 break;

 default:
 double.TryParse(s, NumberStyles.Any, out result);
 if (numStk.Count &gt; 0)
 {
 result = op(result);
 }
 numStk.Push(result);
 break;
 }
 }
 return result;
 }
}

....
var str = " 100.5 + 300.5 - 100 * 10 / 100"; 
str = Regex.Replace(str, @"\s", "", RegexOptions.Multiline);
Stack&lt;string&gt; strStk = new Stack&lt;string&gt;(
 Regex.Split(str, @"([()*+\/-])", RegexOptions.Multiline).Reverse()
);
RPN.Parse(strStk);
</code></pre>

To enable precedence by bracketing a stack of stacks will suffice, such as archived by recursion. Anything between brackets is put on a new stack.
Finally you can support math operations in a clean readable fashion by lambdas.

blocks|key|1457151|text|MathNet.Symbolics|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1457152|using+System;
using+static+MathNet.Symbolics.SymbolicExpression;
using+static+System.Console;
using+static+System.Numerics.Complex;
using+Complex+=+System.Numerics.Complex;

namespace+MathEvaluator
{
++++class+Program
++++{
++++++++static+readonly+Complex+i+=+ImaginaryOne;

++++++++static+void+Main(string[]+args)
++++++++{
++++++++++++var+z+=+Variable("z");
++++++++++++Func<Complex,+Complex>+f+=+Parse("z+*+z").CompileComplex(nameof(z));
++++++++++++Complex+c+=+1+/+2+-+i+/+3;
++++++++++++WriteLine(f(c));


++++++++++++var+x+=+Variable("x");
++++++++++++Func<double,+double>+g+=+Parse("x+*+x+%2B+5+*+x+%2B+6").Compile(nameof(x));
++++++++++++double+a+=+1+/+3.0;
++++++++++++WriteLine(g(a));
++++++++}
++++}
}|code-block|syntax|javascript|1457153|别忘了加载|1457154|<PackageReference+Include="MathNet.Symbolics"+Version="0.20.0"+/>|1457155|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<h1>MathNet.Symbolics</h1>

<pre><code>using System;
using static MathNet.Symbolics.SymbolicExpression;
using static System.Console;
using static System.Numerics.Complex;
using Complex = System.Numerics.Complex;

namespace MathEvaluator
{
 class Program
 {
 static readonly Complex i = ImaginaryOne;

 static void Main(string[] args)
 {
 var z = Variable("z");
 Func&lt;Complex, Complex&gt; f = Parse("z * z").CompileComplex(nameof(z));
 Complex c = 1 / 2 - i / 3;
 WriteLine(f(c));


 var x = Variable("x");
 Func&lt;double, double&gt; g = Parse("x * x + 5 * x + 6").Compile(nameof(x));
 double a = 1 / 3.0;
 WriteLine(g(a));
 }
 }
}
</code></pre>

Don't forget to load 

<pre><code>&lt;PackageReference Include="MathNet.Symbolics" Version="0.20.0" /&gt;
</code></pre>

blocks|key|1672268|text|你可以使用我的Math-Expression-Evaluator库。它支持简单的表达式，如2.5%2B5.9、17.89-2.47%2B7.16、5/2/2%2B1.5*3%2B4.58、带括号的表达式(((9-6/2)*2-4)/2-6-1)/(2%2B24/(2%2B4))和带变量的表达式：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1672269|var+a+=+6;
var+b+=+4.32m;
var+c+=+24.15m;
var+engine+=+new+ExpressionEvaluator();
engine.Evaluate("(((9-a/2)*2-b)/2-a-1)/(2%2Bc/(2%2B4))",+new+{+a,+b,+c});|code-block|syntax|javascript|1672270|您还可以将参数作为命名变量进行传递：|1672271|dynamic+dynamicEngine+=+new+ExpressionEvaluator();

var+a+=+6;
var+b+=+4.5m;
var+c+=+2.6m;

dynamicEngine.Evaluate("(c%2Bb)*a",+a:+6,+b:+4.5,+c:+2.6);|1672272|它支持.Net标准2.0，因此可以在.Net核心以及.Net完整框架项目中使用，并且它没有任何外部依赖。|1672273|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/Giorgi/Math-Expression-Evaluator^0|19|7|1H|F|1X|G|2L|Y|7|P|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1D|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

You can use <a href="https://github.com/Giorgi/Math-Expression-Evaluator" rel="nofollow noreferrer">Math-Expression-Evaluator</a> library that I am author of. It supports simple expressions such as <code>2.5+5.9</code>, <code>17.89-2.47+7.16</code>, <code>5/2/2+1.5*3+4.58</code>, expressions with parentheses <code>(((9-6/2)*2-4)/2-6-1)/(2+24/(2+4))</code> and expressions with variables:

<pre><code>var a = 6;
var b = 4.32m;
var c = 24.15m;
var engine = new ExpressionEvaluator();
engine.Evaluate("(((9-a/2)*2-b)/2-a-1)/(2+c/(2+4))", new { a, b, c});
</code></pre>

You can also pass parameters as named variables:

<pre><code>dynamic dynamicEngine = new ExpressionEvaluator();

var a = 6;
var b = 4.5m;
var c = 2.6m;

dynamicEngine.Evaluate("(c+b)*a", a: 6, b: 4.5, c: 2.6);
</code></pre>

It supports .Net Standard 2.0 so can be used from .Net Core as well as .Net Full Framework projects and it doesn't have any external dependencies.

blocks|key|1672343|text|没有内置的解决方案，但有一些简单的方法可以让它工作。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1672344|现在至少有两个很好的新解决方案:使用符号代数AngouriMath或通用算法库Towel。|offset|length|1672345|AngouriMath|1672346|你可以做到|1672347|using+AngouriMath;
Entity+expr+=+"1+%2B+2+%2B+sqrt(2)";
var+answer+=+(double)expr.EvalNumerical();|code-block|syntax|javascript|1672348|(默认情况下，它以高精度计算，可能也很有用)|1672349|或者编译它|1672350|Entity+expr+=+"1+%2B+2+%2B+sqrt(2)+%2B+x+%2B+y";
Func<double,+double,+double>+someFunc+=+expr.Compile<double,+double,+double>("x",+"y");
Console.WriteLine(someFunc(3,+5));|1672351|这样就可以在时间关键型代码中使用它。|1672352|毛巾|1672353|在这里你可以做到|1672354|using+Towel.Mathematics;
var+expression+=+Symbolics.Parse<double>("(2+%2B+2+*+2+-+(2+%5E+4))+/+2");
Console.WriteLine(expression.Simplify());|1672355|它会将你的表达式直接计算成double。|style|CODE|1672356|安装|1672357|这两个都可以通过Nuget安装：AngouriMath，Towel。|1672358|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/asc-community/AngouriMath|1|https://github.com/ZacharyPatten/Towel|2|https://www.nuget.org/packages/AngouriMath|3|https://www.nuget.org/packages/Towel^0|0|M|B|0|13|5|1|0|0|0|0|0|0|0|0|0|0|0|D|6|0|0|G|B|2|S|5|3|0^^$0|@$1|2|3|4|5|6|7|1O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1P|8|@]|9|@$D|1Q|E|1R|1|1S]|$D|1T|E|1U|1|1V]]|A|$]]|$1|F|3|G|5|6|7|1W|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1X|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1Y|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|20|8|@]|9|@]|A|$]]|$1|S|3|T|5|L|7|21|8|@]|9|@]|A|$M|N]]|$1|U|3|V|5|6|7|22|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|23|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|24|8|@]|9|@]|A|$]]|$1|10|3|11|5|L|7|25|8|@]|9|@]|A|$M|N]]|$1|12|3|13|5|6|7|26|8|@$D|27|E|28|14|15]]|9|@]|A|$]]|$1|16|3|17|5|6|7|29|8|@]|9|@]|A|$]]|$1|18|3|19|5|6|7|2A|8|@]|9|@$D|2B|E|2C|1|2D]|$D|2E|E|2F|1|2G]]|A|$]]|$1|1A|3|-4|5|6|7|2H|8|@]|9|@]|A|$]]]|1B|$1C|$5|1D|1E|1F|A|$1G|1H]]|1I|$5|1D|1E|1F|A|$1G|1J]]|1K|$5|1D|1E|1F|A|$1G|1L]]|1M|$5|1D|1E|1F|A|$1G|1N]]]]

There's no built-in solution, but there are easy ways to make it work.
There are at least two good new solutions for the problem now: using symbolic algebra <a href="https://github.com/asc-community/AngouriMath" rel="nofollow noreferrer">AngouriMath</a> or general purpose algorithm library <a href="https://github.com/ZacharyPatten/Towel" rel="nofollow noreferrer">Towel</a>.
<h3>AngouriMath</h3>
You can do
<pre class="lang-cs prettyprint-override"><code>using AngouriMath;
Entity expr = &quot;1 + 2 + sqrt(2)&quot;;
var answer = (double)expr.EvalNumerical();
</code></pre>
(by default it computes in high-precision, might be useful too)
Or compile it
<pre class="lang-cs prettyprint-override"><code>Entity expr = &quot;1 + 2 + sqrt(2) + x + y&quot;;
Func&lt;double, double, double&gt; someFunc = expr.Compile&lt;double, double, double&gt;(&quot;x&quot;, &quot;y&quot;);
Console.WriteLine(someFunc(3, 5));
</code></pre>
so that it could be used in time-critical code.
<h3>Towel</h3>
Here you can do
<pre class="lang-cs prettyprint-override"><code>using Towel.Mathematics;
var expression = Symbolics.Parse&lt;double&gt;(&quot;(2 + 2 * 2 - (2 ^ 4)) / 2&quot;);
Console.WriteLine(expression.Simplify());
</code></pre>
which would directly compute your expression into <code>double</code>.
<h3>Installation</h3>
Both can be installed via Nuget: <a href="https://www.nuget.org/packages/AngouriMath" rel="nofollow noreferrer">AngouriMath</a>, <a href="https://www.nuget.org/packages/Towel" rel="nofollow noreferrer">Towel</a>.

blocks|key|1672413|text|在github上试用我的数学库|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1672414|存储库：https://github.com/matheval/expression-evaluator-c-sharp|offset|length|1672415|nuget：https://www.nuget.org/packages/org.matheval/|1672416|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/matheval/expression-evaluator-c-sharp|1|https://www.nuget.org/packages/org.matheval/^0|0|4|1K|0|0|6|18|1|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@$D|T|E|U|1|V]]|A|$]]|$1|F|3|G|5|6|7|W|8|@]|9|@$D|X|E|Y|1|Z]]|A|$]]|$1|H|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]|P|$5|K|L|M|A|$N|Q]]]]

Try my matheval library on github
repo: <a href="https://github.com/matheval/expression-evaluator-c-sharp" rel="nofollow noreferrer">https://github.com/matheval/expression-evaluator-c-sharp</a>
nuget: <a href="https://www.nuget.org/packages/org.matheval/" rel="nofollow noreferrer">https://www.nuget.org/packages/org.matheval/</a>

If I have a string with a valid math expression such as:

<pre><code>String s = "1 + 2 * 7";
</code></pre>

Is there a built in library/function in .NET that will parse and evaluate that expression for me and return the result? In this case 15.

Is there a string math evaluator in .NET?

编译器

Windows

如果我有一个包含有效数学表达式的字符串，例如：String s = "1 + 2 * 7";.NET中有没有内置库/函数可以帮我解析和计算表达式并返回结果？在本例中为15。

问.NET中有字符串数学计算器吗？
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