Evaluate mathematical expression from a string using VB

Question

I want to calculate a arithmetic expression from a string using VB, any ideas ?

As an example : "x+2" from a textbox, I want to evaluate the expression

I think you mean you want to execute it as an *arithmetic* expression. A *regular* expression is [something completely different](http://en.wikipedia.org/wiki/Regular_expression). I am sure you knew that already — MarkJ, Nov 01 '12 at 14:10
possible duplicate of [Doing math in vb.net like Eval in javascript](http://stackoverflow.com/questions/1452282/doing-math-in-vb-net-like-eval-in-javascript) — Boann, Dec 25 '14 at 00:26
Does this answer your question? [How to evaluate a math expression given in string form?](https://stackoverflow.com/questions/3422673/how-to-evaluate-a-math-expression-given-in-string-form) — duffymo, May 10 '23 at 19:09

score 23 · Answer 1 · answered Jan 19 '17 at 15:41

23

Dim equation As String = "2+6/2"
Dim result = New DataTable().Compute(equation, Nothing)

answered Jan 19 '17 at 15:41

Andrew

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This answer doesn't require an extra library to added to the project:) – craigster Feb 24 '17 at 16:52
1

@Andrew you're amazing... thanks mate. – Cameron B Mar 20 '22 at 22:50

score 12 · Accepted Answer · answered Nov 01 '12 at 14:05

12

you can use NCalc for this. It also accepts parameters like x, y, z,...

Dim e As Expression = new Expression("2 + 3 * 5")
Msgbox(17 = e.Evaluate())

answered Nov 01 '12 at 14:05

John Woo

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@JohanLarsson sorry, i have no idea :( – John Woo Nov 01 '12 at 14:12
I think No. (*not really sure*) . – John Woo Nov 01 '12 at 14:15

antony thomas · Answer 3 · 2016-12-26T16:26:18.597

You can use mxparser library for this purpose.Give a reference to mxparser.dll in your project by clicking ADD Reference button of Microsoft Visual Studio.The mxparser library source code or latest dll file can be from www.mathparser.org.The mXparser is a Math Parser for Java, Android, C# .NET (CLS) Libraries.

Imports org.mariuszgromada.math.mxparser
Private Function evaluate(ByVal str As String) AS Double
Dim expr As Expression = New Expression(str)
DIM d1 As Double
d1=0
d1=expr.calculate()
return d1
End Function

Call to the function can be as follows.

DIM str as String
str=""
str=((45^5)/45))*(5*6)

Dim d as Double
d=0
d=evaluate(str)
MsgBox(" The result of the expression is   " + d.ToString)

For mXparser ( http://mathparser.org/ ) there is even nice "hello world" tutorial for VB :-) http://mathparser.org/mxparser-hello-world/mxparser-hello-world-visual-basic/ — Leroy Kegan, Apr 21 '17 at 20:51

score 0 · Answer 4 · answered May 10 '23 at 18:54

I found this else where, it provides the full functionality of VBScript, and its not an external library.

'Set a reference in your app to "Microsoft Script Control 1.0"
'It is under the COM tab in references, not in the .NET tab
'
Dim SC As New MSScriptControl.ScriptControl With {.Language = "VBSCRIPT"}
Dim Formula As String = "(1+2)*(3+4)"
Try
    Dim Result As Double = Convert.ToDouble(SC.Eval(Formula))
    MessageBox.Show("Math success, " & Formula & " = " & Result.ToString)
Catch ex As Exception
    MessageBox.Show("Not a valid math formula for a double.")
End Try

Evaluate mathematical expression from a string using VB

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