1public static int WeekOfMonth(DateTime dtSel,bool sundayStart)
 2{
 3    //如果要判断的日期为1号，则肯定是第一周了
 4    if (dtSel.Day == 1)
 5        return 1;
 6    else
 7    {
 8        //得到本月第一天
 9        DateTime dtStart = new DateTime(dtSel.Year, dtSel.Month, 1);
10        //得到本月第一天是周几
11        int dayofweek = (int)dtStart.DayOfWeek;
12
13        //如果不是以周日开始，需要重新计算一下dayofweek，详细风DayOfWeek枚举的定义
14        if (!sundayStart)
15        {
16            dayofweek = dayofweek - 1;
17
18            if (dayofweek < 0)
19                dayofweek = 7;
20        }
21
22        //得到本月的第一周一共有几天
23        int startWeekDays = 7 - dayofweek;
24
25        //如果要判断的日期在第一周范围内，返回1
26        if (dtSel.Day <= startWeekDays)
27            return 1;
28        else
29        {
30            int aday = dtSel.Day + 7 - startWeekDays;
31            return aday / 7 + (aday % 7 > 0 ? 1 : 0);
32        }
33    }
34}