Eval C#運算式計算

Console.WriteLine(Evaluator.Eval("1+2+3+4+5+6+7+8+9"));//45Console.WriteLine(Evaluator.Eval("(1+1)/2*3"));Console.WriteLine(Evaluator.Eval("((10-2)/2+1)*3"));//15

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.CodeDom.Compiler;
using System.Reflection;

namespace Eval_Demo
{
    /// <summary>
    /// 動態求值
    /// </summary>
    public class Evaluator
    {
        /// <summary>
        /// 計算結果,如果運算式出錯則拋出異常
        /// </summary>
        /// <param name="statement">運算式,如"1+2+3+4"</param>
        /// <returns>結果</returns>
        public static object Eval(string statement)
        {
            return _evaluatorType.InvokeMember(
                        "Eval",
                        BindingFlags.InvokeMethod,
                        null,
                        _evaluator,
                        new object[] { statement }
                     );
        }

        static Evaluator()
        {
            //構造JScript的編譯驅動代碼
            CodeDomProvider provider = CodeDomProvider.CreateProvider("JScript");

            CompilerParameters parameters;
            parameters = new CompilerParameters();
            parameters.GenerateInMemory = true;

            CompilerResults results;
            results = provider.CompileAssemblyFromSource(parameters, _jscriptSource);

            Assembly assembly = results.CompiledAssembly;
            _evaluatorType = assembly.GetType("Evaluator");

            _evaluator = Activator.CreateInstance(_evaluatorType);
        }

        private static object _evaluator = null;
        private static Type _evaluatorType = null;

        /// <summary>
        /// JScript代碼
        /// </summary>
        private static readonly string _jscriptSource =
            @"class Evaluator
              {
                  public function Eval(expr : String) : String 
                  { 
                     return eval(expr); 
                  }
              }";
    }

}