C#四种Eval测试结果：不要用CodeDom做大批量的表达式四则运算

有时候需要表达式运算，如

String strExpression="-12 * ( - 2.2 + 7.7 ) - 44 * 2";

网上找的，一般是利用CodeDom，见

http://www.codeproject.com/csharp/runtime_eval.asp

简化为：

System.CodeDom.Compiler.ICodeCompiler comp = (new Microsoft.CSharp.CSharpCodeProvider().CreateCompiler());

System.CodeDom.Compiler.CompilerParameters cp = new System.CodeDom.Compiler.CompilerParameters();

object qswhEval2(string Expression){

StringBuilder code = new StringBuilder();

code.Append("using System; \n");

code.Append("namespace ADOGuy { \n");

code.Append(" public class _Evaluator { \n");

code.Append(" public object __foo() ");

code.Append("{ ");

code.AppendFormat(" return ({0}); ", Expression);

code.Append("}\n");

code.Append("} }");

System.CodeDom.Compiler.CompilerResults cr = comp.CompileAssemblyFromSource(cp, code.ToString());