C#获取当前星期几，使用DateTime.Now.DayOfWeek函数。
返回枚举常数，指示星期几。该属性值的范围从零（表示星期日）到六（表示星期六）。
string s = DateTime.Now.DayOfWeek.ToString();//值是"Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"
int w=Convert.ToInt32(DateTime.Now.DayOfWeek);//值是0至6
