获取当天为一年中的第几周

方法一:

using System.Globalization;

TaiwanCalendar tc=new TaiwanCalendar();
     int Now_num=tc.GetWeekOfYear(DateTime.Now,CalendarWeekRule.FirstFullWeek,DayOfWeek.Sunday);
//获取当前日期是本年的第几周

方法二:

private int GetWeekOrderOfDate(DateTime Date)
{
            //当天所在的年份
            int year = Date.Year;
            //当年的第一天
             DateTime firstDay = new DateTime(year, 1, 1);
            //当年的第一天是星期几
            int firstOfWeek = Convert.ToInt32(firstDay.DayOfWeek);
            //当年第一周的天数
            int firstWeekDayNum = 7 - firstOfWeek;
            
            //传入日期在当年的天数与第一周天数的差
            int otherDays = Date.DayOfYear - firstWeekDayNum;
            //传入日期不在第一周内
            if (otherDays > 0)
          {
                int weekNumOfOtherDays;
                if (otherDays % 7 == 0)
                {
                     weekNumOfOtherDays = otherDays / 7;
                 }
                else
                {
                     weekNumOfOtherDays = otherDays / 7 + 1;
                 }

                return weekNumOfOtherDays + 1;
           }
            //传入日期在第一周内
            else
          {
             return 1;
          }
 }