enum 的位置问题
为什么定义一个枚举类型 把它放在命名空间之下 class program之上啊！
经过测试，放在main之前的这2处 均可
namespace student
{
enum Days { Saturday = 1, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };
class Program
{
//enum Days { Saturday = 1, Sunday, Monday, Tuesday, Wednesday, Thursday, Friday };
static void Main(string[] args)
