A simple way to evaluate mathematical expressions using CodeDom

[conipto]

Ok, I searched around quite a bit for something that could do simple math expressions, and found a few complicated examples that utilised the CodeDom namespace in the .NET framework to let C# do all the work for us. This function allows you to execute any C# code on the fly with slight modification, but for this purpose, it's primary function is as a calculator. I put this up here because all of the examples I found were quite lengthy and typically contained alot more code than I needed for this simple task.

To start, you need to either import the following namespaces, or fully qualify several of the variable declarations and method usages in the function. I think it's much cleaner to just import the namespaces:

using System.CodeDom.Compiler;
using Microsoft.CSharp;
using System.Reflection;

Now that you have the namespaces imported into your project, the following function will solve almost all mathematical expressions (Basically anything you could solve in a single line of code)

/// <summary>
        /// A simple function to get the result of a C# expression (basic and advanced math possible)
        /// </summary>
        /// <param name="command">String value containing an expression that can evaluate to a double.</param>
        /// <returns>a Double value after evaluating the command string.</returns>
        private double ProcessCommand(string command)
        {
            //Create a C# Code Provider
            CSharpCodeProvider myCodeProvider = new CSharpCodeProvider();
            // Build the parameters for source compilation.
            CompilerParameters cp = new CompilerParameters();
            cp.GenerateExecutable = false;//No need to make an EXE file here.
            cp.GenerateInMemory = true;   //But we do need one in memory.
            cp.OutputAssembly = "TempModule"; //This is not necessary, however, if used repeatedly, causes the CLR to not need to 
                                              //load a new assembly each time the function is run.
            //The below string is basically the shell of a C# program, that does nothing, but contains an
            //Evaluate() method for our purposes.  I realize this leaves the app open to injection attacks, 
            //But this is a simple demonstration.
            string TempModuleSource = "namespace ns{" +
                                      "using System;" +
                                      "class class1{" +
                                      "public static double Evaluate(){return " + command + ";}}} ";  //Our actual Expression evaluator
                                     
            CompilerResults cr = myCodeProvider.CompileAssemblyFromSource(cp,TempModuleSource);
            if (cr.Errors.Count > 0)
            {
                //If a compiler error is generated, we will throw an exception because 
                //the syntax was wrong - again, this is left up to the implementer to verify syntax before
                //calling the function.  The calling code could trap this in a try loop, and notify a user 
                //the command was not understood, for example.
                throw new ArgumentException("Expression cannot be evaluated, please use a valid C# expression");
            }
            else
            {
                MethodInfo Methinfo = cr.CompiledAssembly.GetType("ns.class1").GetMethod("Evaluate");
                return (double)Methinfo.Invoke(null, null);
            }
        }

It is a little on the slow side, but does work. Any suggestions on how to speed up the process are encouraged.

Here are some sample calls to the function and their outputs:

Console.WriteLine(ProcessCommand("1+1").ToString()); //Displays 2
            Console.WriteLine(ProcessCommand("Math.PI").ToString()); //Displays 3.14159265358979
            Console.WriteLine(ProcessCommand("Math.Abs(-22)").ToString()); //Displays 22
            Console.WriteLine(ProcessCommand("3-4+6+7+22/3+66*(55)").ToString()); //Displays 3649

I will put a VB.NET version up later this week if anyone thinks it could be usefull.

Bill