How do I utilize string "*" or "\" as mathematical operators?

Question

I want to use "*" or "\" as mathematical operators as such:

"I am going to clarify"

dim tbox as textbox
tbox.text = "*"

dim i as integer = 8 tbox.text 3

"End Clarify"

dim [mult] as string = "*"
dim [div] as string = "\"


dim i as integer = 8 [mult] 3

and the result would be i is equal to 24

or

dim i as integer = 8 [div] 2 

and the result would be i is equal to 4

Can anyone solve this in one line without building a long, complex function? I would also like for this to be something that is already a part of the VB.NET structure and doesn't require an import.

If such a solution does not exist how do I do it with a function or .dll import?

Answer 1

OK I'm a bit lost, why wouldn't you just use the operators directly?

i.e.

Dim i as integer = 8 * 3

Answer 2

You could eval an entire string like "8*3" using a ScriptControl:

http://www.devx.com/vb2themax/Tip/18773

Pretty dangerous, though...you would need to throughly sanitize any user input to make sure it's only math they are attempting.

Answer 3

You can use CodeDom to evaluate expressions. The expression in your example would be "8 * 3", or "8" + tbox.Text + "3".

Here's an example of how to do this in VB.NET. The function is certainly more than a one liner, but calling it will be simple.

Answer 4

Can anyone solve this in one line without building a long, complex function?

Perhaps, yes, but I think a small function is much better:

Function Compute(a as integer, oper as String, b as integer) as integer
  If oper = "*" Then
    return a*b
  ElseIf oper = "\" Then
    Return a\b
  Else
    Throw New InvalidOperationException()
  End If
End Function

If you really want a one-liner you can use the If() function:

Dim i As Integer = If(oper = "*", a*b, a\b)

This will not check for invalid operators.

Answer 5

Insert This into where you want to evaluate.

dim [mult] as string = "*"
dim [div] as string = "\"


'dim i as integer = 8 [mult] 3

op = mult

dim i As Integer = Eval("8" & op & "3")

'i is your result


  Private Function Eval(ByVal command As String) As Object
    Dim MyProvider As New VBCodeProvider 'Create a new VB Code Compiler
    Dim cp As New CodeDom.Compiler.CompilerParameters     'Create a new Compiler parameter object.

    cp.GenerateExecutable = False        'Don't create an object on disk
    cp.GenerateInMemory = True           'But do create one in memory.

    'If cp.OutputAssembly is used with a VBCodeProvider, it seems to want to read before it is executed. 

    'See C# CodeBank example for explanation of why it was used.



    'the below is an empty VB.NET Project with a function that simply returns the value of our command parameter.

    Dim ClassName As String = "class" & Now.Ticks

    Dim TempModuleSource As String = "Imports System" & Environment.NewLine & _
                                     "Namespace ns " & Environment.NewLine & _
                                     "    Public Class " & ClassName & Environment.NewLine & _
                                     "        Public Shared Function Evaluate()" & Environment.NewLine & _
                                     "            Return (" & command & ")" & Environment.NewLine & _
                                     "        End Function" & Environment.NewLine & _
                                     "    End Class" & Environment.NewLine & _
                                     "End Namespace"

    'Create a compiler output results object and compile the source code.

    Dim cr As CodeDom.Compiler.CompilerResults = MyProvider.CompileAssemblyFromSource(cp, TempModuleSource)

    If cr.Errors.Count > 0 Then

      'If the expression passed is invalid or "", the compiler will generate errors.

      'Throw New ArgumentOutOfRangeException("Invalid Expression - please use something VB could evaluate")
      Return Nothing
    Else

      'Find our Evaluate method.
      Dim methInfo As Reflection.MethodInfo = cr.CompiledAssembly.GetType("ns." & ClassName).GetMethod("Evaluate")

      'Invoke it on nothing, so that we can get the return value
      Return methInfo.Invoke(methInfo, New Object() {})
    End If
  End Function

Answer 6

This is not worth even trying. It will eat up so much CPU just to do the operation you could have manually typed it.

Answer 7

This is confusing, are you saying you want to use multiply and divide as operators in VB.NET?

The can be accomplished with dim i as integer = 8*9

Answer 8

I believe you need some very complex logic to accommodate this omission from Microsoft. Here's how to do it in C#

http://www.c-sharpcorner.com/UploadFile/mgold/CodeDomCalculator08082005003253AM/CodeDomCalculator.aspx