返回一年中的第几周

    private int weekNumber()
    {            
        string firstDateText = DateTime.Now.Year.ToString() + "年1月1日";
        DateTime firstDay = Convert.ToDateTime(firstDateText);
        int theday;
        if (firstDay.DayOfWeek == DayOfWeek.Sunday || firstDay.DayOfWeek == DayOfWeek.Monday)
        {
            theday = 0;
        }
        else if (firstDay.DayOfWeek == DayOfWeek.Tuesday)
        {
            theday = 1;
        }
        else if (firstDay.DayOfWeek == DayOfWeek.Wednesday) { theday = 2; }
        else if (firstDay.DayOfWeek == DayOfWeek.Thursday) { theday = 3; }
        else if (firstDay.DayOfWeek == DayOfWeek.Friday)
        {
            theday = 4;
        }
        else
        {
            theday = 5;
        }
        DateTime nowDate = DateTime.Now;
        int weekNum = (nowDate.DayOfYear + theday) / 7 + 1;
        return weekNum;
    }