Evaluating the Expression in VB.net

Question

Hi...

I need to evaluate the expression which is given in TextBox. The expression can be any math function or simple arithmetic expression. I am sure that there will be some function to do this directly because in older development software it is available. 

Please help..

Thanks and Regards..

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Shrinidhi Acharya

Answer 1

Hi shrinidhi,

Thanks for you post.

As for you issue, I’d like to do some clarify.

>>because in older development software it is available.

Would you like to share more information about this? Do some math methods are available in old versions and not available or caused some exception at now?

It will be better if you can share the code about the expression.

I look forward your reply.

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Mark Liu-lxf [MSFT]
MSDN Community Support | Feedback to us

Answer 2

There is some discussion here:
http://social.msdn.microsoft.com/Forums/en/vblanguage/thread/41466b93-56cb-4dd0-8a16-d53aec3c4a2f

There is a complete project here:
http://www.codeproject.com/Articles/9519/An-expression-evaluator-written-in-VB-NET

and some more here:
http://www.freevbcode.com/ShowCode.asp?ID=1263

Answer 3

Hi,

For a simple mathematical expression try the .Compute()

method for a DataTable.

'

Add one Button and one TextBox to your Form to try this code please.>>

'

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        TextBox1.Text = "2*3+8"

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim dt As New DataTable
        Dim result As Decimal

        Try
            result = Convert.ToDecimal(dt.Compute(TextBox1.Text, ""))
            MessageBox.Show(result.ToString, "Result = ")
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try

    End Sub

End Class

 

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Regards,

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Answer 4

The datatable or script host solutions are probably the most efficient.

A CodeDom solution might be more versitle but will incur more overhead.  A full parser/lexer that supports all possible expression syntax could be a lot of work, could be slow if it is not implemented properly, and would be overkill for simple expressions.

If you expect all of the expressions to be simple, use the datatable as suggested by John Oliver.  For more complex expressions, the script host is probably the way to go.

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Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 5

dangit .paul._ I wondered why kept getting an error trying to propose this post!  You snuck in and beat me to it.  =)

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Reed Kimble - "When you do things right, people won't be sure you've done anything at all"

Answer 6

Hi John Anthony Oliver,

Your solution works superfine with arithmetic expression but if i need to insert mathematical expressions like sin(), cos() etc.. it does not work..

 

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Shrinidhi Acharya

Answer 7

Hi John Anthony Oliver,

Your solution works superfine with arithmetic expression but if i need to insert mathematical expressions like sin(), cos() etc.. it does not work.

If you want to use those types of functions you will need to look at some of the other options that have been suggested.   Each evaluator will support a different set of functionality.