Evaluating String Expression - VB.Net

Posted Date: 11 Feb 2007	Resource Type: Articles	Category: .NET Framework
Author: Pandian S	Member Level: Gold
Rating:	Points: 10

This example shows how to evaluate mathematical expressions using code in VB .NET.

There are THREE steps to be done
1.Creating JavaScript Package
Open Notepad --> Enter the following Code .

package JPackage
{
Class JClass
{
function Evaluate(strExp : String) : String
{
return eval(strExp);
}
}
}

Save the aboce code with the name of 'JPackage.js'
Ex: C:\JPackage.js

2. Compiling the Package
Open .NET Command Prompt --> Do the following
C:\> jsc /t:library JPackage.js (Press ENTER)
Now, One .Dll file created (Ex: JPackage.dll)

3. Reference the .DLL file with our Project
In Solution Explorer --> Right Click on 'References' --> Add Reference..
In .NET Tab, Click Browse Button and Locate the Dll which you have created 'C:\JPackage.dll'.

Note
This solution require an aditional Namespace called 'Microsoft.JScript'
In Solution Explorer --> Right Click on 'References' --> Add Reference..
Select 'Microsoft.JScript' and Click 'Select' button and click 'OK'.

.Net Code

Imports JPackage

Dim jsp As New JClass()
Dim F As Double = 50.5
Dim strEval As String = "(" & F & " - 32.0)*5.0/9.0"
MsgBox(jsp.Evaluate(strEval))

Input:
Dim strEval As String = "(50.5 - 32.0)*5.0/9.0"

Result:
10.277777777777778

Input:
Dim strEval As String = "(1 < 3) & (3 < 1)"

Result:
0 (False)

Happy Coding
Pandian S

Responses

Author: Stephen M 18 Jul 2007

Member Level: Bronze Points : 0

I have a feeling this has more to do with my compiler, but both the ASP.NET v1.1 and v2.0 compilers won't compile the JScript:

c:\JPackage.js(3,7) : error JS1004: Expected ';'
c:\JPackage.js(10,1) : error JS1002: Syntax error
c:\JPackage.js(4,1) : error JS1234: Only type and package definitions are allowed inside a library

This is exactly what I need and is a perfect quick solution for what I need. So I hope you can help me determine my compilation issue!

Author: Stephen M 18 Jul 2007

Member Level: Bronze Points : 0

OK ... I figured it out ... simple as I expected

The class declaration must be "class" with a lower case 'c' ... I simply did a cut & paste and without any prior JScript knowledge it didn't jump out at me right away.

Anyway ... this is here for anyone else who needs this solution!

Author: Joe 13 Jul 2009

Member Level: Bronze Points : 2

I modified the code a little because the new vb.net requires strongly named binaries. Also this now supports advanced math including trig and exponential functions

import System.Reflection
[assembly:AssemblyKeyFile("C:\\mpkey.snk")]
[assembly:AssemblyVersion("1.0.0.1")]
package JPackage
{
class JClass
{
function Evaluate(strExp : String) : String
{
with(Math)
{
return eval(strExp);
}
}
}
}

Author: R.Jaya kumar (JK) 15 Jul 2009

Member Level: Diamond Points : 0

error comes here check this jpg file

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