Evaluate function in C# .Net as Eval() function in Javascript

Evaluate function in C# .Net Alternate methods to evaluate a string and retrieve a result as Eval() function in Javascript.

Eval() function in Visual basic or javascript evaluates a string and executes it as if it was script code. Thereby we can pass a string containing a valid expression and retrieve a result on execution.

Unfortunately, neither C# nor Visual Basic .NET has the same functionality. I think this is a big difference between a compiled language and a interpreted one.

I found two simple methods in .Net to implement Evaluate function which would evaluates a string and gives the result.

Method 1 :

	public static double Evaluate(string expression)
        {
            return (double)new System.Xml.XPath.XPathDocument
            (new System.IO.StringReader("<r/>")).CreateNavigator().Evaluate
            (string.Format("number({0})", new
            System.Text.RegularExpressions.Regex(@"([\+\-\*])").Replace(expression, " ${1} ")
.Replace("/", " div ").Replace("%", " mod ")));
        }

In Method 1 System.Text.RegularExpressions.Regex helps in giving space between operator and also to replace "/" operator to div and "%" operator to mod. XPathNavigator.Evaluate method evaluates the string representing an XPath expression and returns the typed result.

Method 2 :

	public static double Evaluate(string expression)
        {
            System.Data.DataTable table = new System.Data.DataTable();
            table.Columns.Add("expression", string.Empty.GetType(), expression);
            System.Data.DataRow row = table.NewRow();
            table.Rows.Add(row);
            return double.Parse((string)row["expression"]);
        }

In Method 2 DataColumn.Expression in System.Data.DataTable is used to create a default row with required expression. Thereby DataTable calculate the values in a column and gives the evaluated result. Resultant datatype for Evaluate function in method 2 can changed to evaluate boolean expression and to get boolean results.

System.Console.WriteLine(Evaluate("2 * 4"));

Result would be "8".