using System;

// see: https://stackoverflow.com/questions/13071823/convert-expression-from-a-textbox-to-math-expression-in-code-behind/13071974#13071974

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Eval("15 * (3 + 5) / (7 - 2)"));

    }

    public static string Eval(string expr)

    {

        var temp = new System.Data.DataTable();

        string result = null;

        try

        {           

            result = $"{temp.Compute(expr, string.Empty)}"; 

        }

        catch (System.Data.EvaluateException ex)

        {

          if (ex.Message.ToLower().Contains("cannot find column"))

                throw new System.Data.SyntaxErrorException($"Syntax error: Invalid expression: '{expr}'."

                                               + " Variables as operands are not supported.");

          else

                throw;

        }

        return result;

    }

}