C#中周，月，第几周，周开始结束时间de方法总结

    private  static int getWeekNumInMonth(DateTime daytime)  
            {  
                int dayInMonth = daytime.Day;  
                //本月第一天  
                DateTime firstDay = daytime.AddDays(1 - daytime.Day);  
                //本月第一天是周几  
                int weekday = (int)firstDay.DayOfWeek == 0 ? 7 : (int)firstDay.DayOfWeek;  
                //本月第一周有几天  
                int firstWeekEndDay = 7 - (weekday - 1);  
                //当前日期和第一周之差  
                int diffday = dayInMonth - firstWeekEndDay;  
                diffday = diffday > 0 ? diffday : 1;  
                //当前是第几周,如果整除7就减一天  
                int WeekNumInMonth = ((diffday % 7) == 0  
                 ? (diffday / 7 - 1)  
                 : (diffday / 7)) + 1 + (dayInMonth > firstWeekEndDay ? 1 : 0);  
                return WeekNumInMonth;  
            }  

    GregorianCalendar gc = new GregorianCalendar();  
               int weekOfYear = gc.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstDay, DayOfWeek.Monday);  
               Console.WriteLine(weekOfYear);  
               Console.ReadLine();  

 /// <summary>
             /// 获得本月有几周
             /// </summary>
             /// <param name="a"></param>
             /// <returns></returns>
             public  void NumWeeks(DateTime dt)
             {
                 //年
                 int year = dt.Year;
                 //月
                 int month = dt.Month;
                 //当前月第一天
                 DateTime weekStart = new DateTime(year, month, 1);
                 //该月的最后一天
                 DateTime monEnd = weekStart.AddMonths(1).AddDays(-1);
                 int i = 1;
                 //当前月第一天是星期几
                 int dayOfWeek = Convert.ToInt32(weekStart.DayOfWeek.ToString("d"));
                 //该月第一周结束日期
                 DateTime weekEnd = dayOfWeek == 0 ? weekStart : weekStart.AddDays(7 - dayOfWeek);

                 richTextBox2.Text += "第" + i + "周起始日期： " + weekStart.ToShortDateString() + "   结束日期： " + weekEnd.ToShortDateString() + "\n";

                 //当日期小于或等于该月的最后一天
                 while (weekEnd.AddDays(1) <= monEnd)
                 {
                     i++;
                     //该周的开始时间
                     weekStart = weekEnd.AddDays(1);
                     //该周结束时间
                     weekEnd = weekEnd.AddDays(7) > monEnd ? monEnd : weekEnd.AddDays(7);

                     richTextBox2.Text += "第" + i + "周起始日期： " + weekStart.ToShortDateString() + "   结束日期： " + weekEnd.ToShortDateString() + "\n";
                 }

                 richTextBox2.Text += year + "年" + month + "月共有" + i + "周\n";
             }