Doing math in vb.net like Eval in javascript

There’s a shortcut for limited (ie. simple) math expressions by using the DataTable.Compute method. Obviously, this isn’t robust (limited functionality) and feels hackish to misuse the DataTable for this purpose, but I figured I would add to the current answers.

Example:

var result = new DataTable().Compute("3+(7/3.5)", null); // 5

“Sin(90)” wouldn’t work with this approach. Refer to the DataColumn.Expression Property page for a list of supported functions, specifically under the “Aggregates” section.

Using the System.CodeDom namespace is an option.

Some helpful links:

CodeDom Calculator
Evaluating mathematical expressions using CodeDom
Related SO question: Is there a string math evaluator in .NET?

EDIT: to address your comment, here is an approach to demonstrate replacing trigonometric functions with their equivalent Math class methods.

string expression = "(Sin(0) + Cos(0)+Tan(0)) * 10";
string updatedExpression = Regex.Replace(expression, @"(?<func>Sin|Cos|Tan)\((?<arg>.*?)\)", match =>
            match.Groups["func"].Value == "Sin" ? Math.Sin(Int32.Parse(match.Groups["arg"].Value)).ToString() :
            match.Groups["func"].Value == "Cos" ? Math.Cos(Int32.Parse(match.Groups["arg"].Value)).ToString() :
            Math.Tan(Int32.Parse(match.Groups["arg"].Value)).ToString()
        );
var result = new DataTable().Compute(updatedExpression, null); // 10

VB.NET

Dim expression As String = "(Sin(0) + Cos(0)+Tan(0)) * 10"
Dim updatedExpression As String = Regex.Replace(expression, "(?<func>Sin|Cos|Tan)\((?<arg>.*?)\)", Function(match As Match) _
        If(match.Groups("func").Value = "Sin", Math.Sin(Int32.Parse(match.Groups("arg").Value)).ToString(), _
        If(match.Groups("func").Value = "Cos", Math.Cos(Int32.Parse(match.Groups("arg").Value)).ToString(), _
        Math.Tan(Int32.Parse(match.Groups("arg").Value)).ToString())) _
        )
Dim result = New DataTable().Compute(updatedExpression, Nothing)

Note, however, that you need to know the contents of the “arg” group. I know they are ints, so I used Int32.Parse on them. If they are a combination of items then this simple approach won’t work. I suspect you will constantly need to band-aid the solution if it gets too complicated with more unsupported function calls, in which case the CodeDom approach or others may be more suitable.

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