Is there any way to parse a string in vb.net (like, built in methods), that can do math like Eval can? For example, 3+(7/3.5) as a string would return 2.
I am not asking for you to code this for me, I just want to know if there is a built in way to do this, if there is not I will code it myself.
I can wager that it would not be able to parse stuff like Sin(90) on its own, and I understand that would need to be replaced by Math.Sin(90).
If there is a built in method, how do you use it?
There's a shortcut for limited (ie. simple) math expressions by using the DataTable.Compute method. Obviously, this isn't robust (limited functionality) and feels hackish to misuse the DataTable for this purpose, but I figured I would add to the current answers.
Example:
var result = new DataTable().Compute("3+(7/3.5)", null); // 5 "Sin(90)" wouldn't work with this approach. Refer to the DataColumn.Expression Property page for a list of supported functions, specifically under the "Aggregates" section.
Using the System.CodeDom namespace is an option.
Some helpful links:
EDIT: to address your comment, here is an approach to demonstrate replacing trigonometric functions with their equivalent Math class methods.
C#
string expression = "(Sin(0) + Cos(0)+Tan(0)) * 10"; string updatedExpression = Regex.Replace(expression, @"(?Sin|Cos|Tan)\((?.*?)\)", match => match.Groups["func"].Value == "Sin" ? Math.Sin(Int32.Parse(match.Groups["arg"].Value)).ToString() : match.Groups["func"].Value == "Cos" ? Math.Cos(Int32.Parse(match.Groups["arg"].Value)).ToString() : Math.Tan(Int32.Parse(match.Groups["arg"].Value)).ToString() ); var result = new DataTable().Compute(updatedExpression, null); // 10 VB.NET
Dim expression As String = "(Sin(0) + Cos(0)+Tan(0)) * 10" Dim updatedExpression As String = Regex.Replace(expression, "(?Sin|Cos|Tan)\((?.*?)\)", Function(match As Match) _ If(match.Groups("func").Value = "Sin", Math.Sin(Int32.Parse(match.Groups("arg").Value)).ToString(), _ If(match.Groups("func").Value = "Cos", Math.Cos(Int32.Parse(match.Groups("arg").Value)).ToString(), _ Math.Tan(Int32.Parse(match.Groups("arg").Value)).ToString())) _ ) Dim result = New DataTable().Compute(updatedExpression, Nothing) Note, however, that you need to know the contents of the "arg" group. I know they are ints, so I used Int32.Parse on them. If they are a combination of items then this simple approach won't work. I suspect you will constantly need to band-aid the solution if it gets too complicated with more unsupported function calls, in which case the CodeDom approach or others may be more suitable.
Here is a way to evaluate an expression that I haven't seen mentioned anywhere else: use a WebBrowser control and JavaScript's eval():
Option Strict On Imports System.Security.Permissions _ Public Class Form1 Dim browser As New WebBrowser Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load browser.ObjectForScripting = Me 'browser.ScriptErrorsSuppressed = True browser.DocumentText = "" End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim result = browser.Document.InvokeScript("evalIt", New String() {"3+4*5"}) If result IsNot Nothing Then MessageBox.Show(result.ToString()) '23 End If End Sub End Class This CodeProject article might do the trick:
An expression evaluator written in VB.NET
http://www.codeproject.com/KB/vb/expression_evaluator.aspx
There is also this:
http://www.dotnetspider.com/resources/2518-mathematical-expression-expression-evaluate-VB.aspx
I don't know about VB.net built in, but we do stuff like this by linking in the IronPython runtime and passing it the expressions. This is way way faster that using reflection.
One way would be to use the CodeDom namespace to compile it and execute it using reflection. May not be that performant, I don't know.
It's a bit late, but here is exactly what you wanted (make sure you parse the input to make sure there is no statement like 'something + vbcrlf + exec "format c:"' in it):
Usage:
MessageBox.Show(COR.Tools.EvalProvider.Eval("return 8-3*2").ToString()) Class:
'Imports Microsoft.VisualBasic Imports System Namespace COR.Tools Public Class EvalProvider Public Shared Function Eval(ByVal vbCode As String) As Object Dim c As VBCodeProvider = New VBCodeProvider Dim icc As System.CodeDom.Compiler.ICodeCompiler = c.CreateCompiler() Dim cp As System.CodeDom.Compiler.CompilerParameters = New System.CodeDom.Compiler.CompilerParameters cp.ReferencedAssemblies.Add("System.dll") cp.ReferencedAssemblies.Add("System.xml.dll") cp.ReferencedAssemblies.Add("System.data.dll") ' Sample code for adding your own referenced assemblies 'cp.ReferencedAssemblies.Add("c:\yourProjectDir\bin\YourBaseClass.dll") 'cp.ReferencedAssemblies.Add("YourBaseclass.dll") cp.CompilerOptions = "/t:library" cp.GenerateInMemory = True Dim sb As System.Text.StringBuilder = New System.Text.StringBuilder("") sb.Append("Imports System" & vbCrLf) sb.Append("Imports System.Xml" & vbCrLf) sb.Append("Imports System.Data" & vbCrLf) sb.Append("Imports System.Data.SqlClient" & vbCrLf) sb.Append("Imports Microsoft.VisualBasic" & vbCrLf) sb.Append("Namespace MyEvalNamespace " & vbCrLf) sb.Append("Class MyEvalClass " & vbCrLf) sb.Append("public function EvalCode() as Object " & vbCrLf) 'sb.Append("YourNamespace.YourBaseClass thisObject = New YourNamespace.YourBaseClass()") sb.Append(vbCode & vbCrLf) sb.Append("End Function " & vbCrLf) sb.Append("End Class " & vbCrLf) sb.Append("End Namespace" & vbCrLf) Debug.WriteLine(sb.ToString()) ' look at this to debug your eval string Dim cr As System.CodeDom.Compiler.CompilerResults = icc.CompileAssemblyFromSource(cp, sb.ToString()) Dim a As System.Reflection.Assembly = cr.CompiledAssembly Dim o As Object Dim mi As System.Reflection.MethodInfo o = a.CreateInstance("MyEvalNamespace.MyEvalClass") Dim t As Type = o.GetType() mi = t.GetMethod("EvalCode") Dim s As Object s = mi.Invoke(o, Nothing) Return s End Function End Class ' EvalProvider End Namespace