Math operators as dynamic variables - asp.net

Question

I have no idea how I'm going to accomplish this BUT someway, somehow I have to perform calculations dynamically in ASP/VB.NET (Possibly SQL Server). Something like this:
Dim var1, var2 as Integer
Dim Optr as string
var1 = 15
var2 = 25
Optr = +
MyResult(var1, var2, Optr)
...and MyResult should equal 40. How can I do this? Anyone have any ideas? Thanks!

Answer 1

The only way I can think of is a switch case which deals with all possible operators.
If you want to implement something more complicated(with operator presedence) you can use the Shunting Yard Algorithm

Answer 2

I don't have the code specifics, but you if have your vars and operations concatenated as a single string you could parse the string and compile it, given you the proper result.
Check this SO questions and answers here, they discuss a very similar problem (if not the exact same)

Answer 3

I like Paul Sasik's example for a purely .net solution, but another alternative would be to make use of the VBScript engine that's part of windows.
For example (you'll need to add a reference to the COM MSScript control)
Static sc As MSScriptControl.ScriptControl
'---- init the script control once
If sc Is Nothing Then
sc = New MSScriptControl.ScriptControl
sc.Language = "VBScript"
sc.AllowUI = False
End If
Try
Return sc.Eval(Expr)
Catch ex As Exception
'Deal with any error conditions here
End Try
Where Expr is any expression you might want to evaluate.
Granted, this leverages VBScript support, which you might want to avoid, but, depending on your audience, they might be more comfortable with that than .net coding

Answer 4

To allow for arbitrarily complex calculations you could take advantage of .NET's on-fly-compilation features. Here's an article for starters.
For your particular implementation you would construct a calculation string from your input like this:
Dim toCalc as string = var1 & " " & Optr & " " & var2
...and use a process where the calculation would get injected into a dynamically created class that would look something like this: (working console sample based on the CP article)
Imports System.CodeDom.Compiler
Imports System.Reflection
Module Module1
Sub Main()
Dim var1 As Integer = 50
Dim var2 As Integer = 65
Dim Optr As String = "+"
Dim equation As String = var1 & " " & Optr & " " & var2
Dim nl As String = System.Environment.NewLine
Dim dynClass As String = ""
dynClass &= "public class DynamicClass" & nl
dynClass &= " public shared function Calc() as double" & nl
dynClass &= " return " & equation & nl
dynClass &= " end function" & nl
dynClass &= "end class" & nl
Try
Dim params As New CompilerParameters
params.ReferencedAssemblies.AddRange(New String() {"Microsoft.VisualBasic.dll"})
Dim mAssembly As Assembly = New VBCodeProvider().CreateCompiler. _
CompileAssemblyFromSource(params, dynClass).CompiledAssembly
Console.WriteLine("Calculating: " & equation)
Console.WriteLine("SUCCESS! Result: " & mAssembly. _
GetType("DynamicClass"). _
InvokeMember("Calc", _
BindingFlags.InvokeMethod Or _
BindingFlags.Public Or _
BindingFlags.Static, _
Nothing, Nothing, Nothing).ToString())
Catch ex As Exception
Console.WriteLine(ex.Message)
End Try
End Sub
End Module