如果在文本框中输入简单的数学计算式：200+100*290之类的计算式，如何计算出他们的值:

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

namespace ADOGuy
{
    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    public class Evaluator
    {

        public Evaluator(EvaluatorItem[] items)
        {
            ConstructEvaluator(items);
        }

        public Evaluator(Type returnType, string expression, string name)
        {
            EvaluatorItem[] items = { new EvaluatorItem(returnType, expression, name) };
            ConstructEvaluator(items);
        }

        public Evaluator(EvaluatorItem item)
        {
            EvaluatorItem[] items = { item };
            ConstructEvaluator(items);
        }

        private void ConstructEvaluator(EvaluatorItem[] items)
        {
            ICodeCompiler comp = (new CSharpCodeProvider().CreateCompiler());
            CompilerParameters cp = new CompilerParameters();
            cp.ReferencedAssemblies.Add("system.dll");
            cp.ReferencedAssemblies.Add("system.data.dll");
            cp.ReferencedAssemblies.Add("system.xml.dll");
            cp.GenerateExecutable = false;
            cp.GenerateInMemory = true;

            StringBuilder code = new StringBuilder();
            code.Append("using System; \n");
            code.Append("using System.Data; \n");
            code.Append("using System.Data.SqlClient; \n");
            code.Append("using System.Data.OleDb; \n");
            code.Append("using System.Xml; \n");
            code.Append("namespace ADOGuy { \n");
            code.Append("  public class _Evaluator { \n");
            foreach(EvaluatorItem item in items)
            {
                code.AppendFormat("    public {0} {1}() ",
                    item.ReturnType.Name,
                    item.Name);
                code.Append("{ ");
                code.AppendFormat("      return ({0}); ", item.Expression);
                code.Append("}\n");
            }
            code.Append("} }");

            CompilerResults cr = comp.CompileAssemblyFromSource(cp, code.ToString());
            if (cr.Errors.HasErrors)
            {
                StringBuilder error = new StringBuilder();
                error.Append("Error Compiling Expression: ");
                foreach (CompilerError err in cr.Errors)
                {
                    error.AppendFormat("{0}\n", err.ErrorText);
                }
                throw new Exception("Error Compiling Expression: " + error.ToString());
            }
            Assembly a = cr.CompiledAssembly;
            _Compiled = a.CreateInstance("ADOGuy._Evaluator");
        }

        public int EvaluateInt(string name)
        {
            return (int) Evaluate(name);
        }

        public string EvaluateString(string name)
        {
            return (string) Evaluate(name);
        }

        public bool EvaluateBool(string name)
        {
            return (bool) Evaluate(name);
        }

        public object Evaluate(string name)
        {
            MethodInfo mi = _Compiled.GetType().GetMethod(name);
            return mi.Invoke(_Compiled, null);
        }

        static public int EvaluateToInteger(string code)
        {
            Evaluator eval = new Evaluator(typeof(int), code, staticMethodName);
            return (int) eval.Evaluate(staticMethodName);
        }

        static public string EvaluateToString(string code)
        {
            Evaluator eval = new Evaluator(typeof(string), code, staticMethodName);
            return (string) eval.Evaluate(staticMethodName);
        }
    
        static public bool EvaluateToBool(string code)
        {
            Evaluator eval = new Evaluator(typeof(bool), code, staticMethodName);
            return (bool) eval.Evaluate(staticMethodName);
        }

        static public object EvaluateToObject(string code)
        {
            Evaluator eval = new Evaluator(typeof(object), code, staticMethodName);
            return eval.Evaluate(staticMethodName);
        }

        const string staticMethodName = "__foo";
        Type _CompiledType = null;
        object _Compiled = null;

    }//CLASS

    public class EvaluatorItem
    {
        public EvaluatorItem(Type returnType, string expression, string name)
        {
            ReturnType = returnType;
            Expression = expression;
            Name = name;
        }

        public Type ReturnType;
        public string Name;
        public string Expression;
    }//CLASS
}//NAMESPACE