I've solved it, here are the details of the resolved class:

If you enter a simple mathematical formula in a text box: A formula like 200+100*290, how to calculate their value:

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