示例，这样还有个好处就是first=0成为一个不合法的enum，这样可以避免出现忘记初始化。但是要注意enum得顺序递增才能用loop。
enum ProgrammingLanguage{Language_First = 0,CPP = 1,CSharp = 2,Java =3,Language_Last = 4,}class Program{static void Main(string[] args){for (ProgrammingLanguage i = ProgrammingLanguage.Language_First + 1; i < ProgrammingLanguage.Language_Last; i++){Console.WriteLine(i);}}}
