C#关于日期 月 天数 和一年有多少周及根据某年某周获取时间段的计算(转)

        /// 当前月有多少天
         /// </summary>
        /// <param name="y"></param>
        /// <param name="m"></param>
        /// <returns></returns>
        public static int HowMonthDay(int y, int m)
        {
            int mnext;
            int ynext;
            if (m < )
            {
                mnext = m + ;
                ynext = y;
            }
            else
            {
                mnext = ;
                ynext = y + ;
            }
            DateTime dt1 = System.Convert.ToDateTime(y + "-" + m + "-1");
            DateTime dt2 = System.Convert.ToDateTime(ynext + "-" + mnext + "-1");
            TimeSpan diff = dt2 - dt1;
            return diff.Days;
        }

/// <summary>
        /// 得到一年中的某周的起始日和截止日
         /// 年 nYear
        /// 周数 nNumWeek
        /// 周始 out dtWeekStart
        /// 周终 out dtWeekeEnd
        /// </summary>
        /// <param name="nYear"></param>
        /// <param name="nNumWeek"></param>
        /// <param name="dtWeekStart"></param>
        /// <param name="dtWeekeEnd"></param>
        public static void GetWeek(int nYear, int nNumWeek, out   DateTime dtWeekStart, out   DateTime dtWeekeEnd)
        {
            DateTime dt = new DateTime(nYear, , );
            dt = dt + new TimeSpan((nNumWeek - ) * , , , );
            dtWeekStart = dt.AddDays(-(int)dt.DayOfWeek + (int)DayOfWeek.Monday);
            dtWeekeEnd = dt.AddDays((int)DayOfWeek.Saturday - (int)dt.DayOfWeek + );
        }

        /// <summary>
        /// 求某年有多少周
         /// 返回 int
        /// </summary>
        /// <param name="strYear"></param>
        /// <returns>int</returns>
        public static int GetYearWeekCount(int strYear)
        {
            string returnStr = "";

            System.DateTime fDt = DateTime.Parse(strYear.ToString() + "-01-01");
            int k = Convert.ToInt32(fDt.DayOfWeek);//得到该年的第一天是周几
              if (k == )
            {
                int countDay = fDt.AddYears().AddDays(-).DayOfYear;
                int countWeek = countDay /  + ;
                return countWeek;
            }
            else
            {
                int countDay = fDt.AddYears().AddDays(-).DayOfYear;
                int countWeek = countDay /  + ;
                return countWeek;
            }
        }

        /// <summary>
        /// 求当前日期是一年的中第几周
         /// </summary>
        /// <param name="date"></param>
        /// <returns></returns>
        public static int WeekOfYear(DateTime curDay)
        {
            int firstdayofweek = Convert.ToInt32(Convert.ToDateTime(curDay.Year.ToString() + "- " + "1-1 ").DayOfWeek);
            int days = curDay.DayOfYear;
            int daysOutOneWeek = days - ( - firstdayofweek);
            if (daysOutOneWeek <= )
            {
                return ;
            }
            else
            {
                int weeks = daysOutOneWeek / ;
                if (daysOutOneWeek %  != )
                    weeks++;
                return weeks + ;
            }
　　}

(注：转自http://www.cnblogs.com/yuanermen/archive/2008/07/14/1242853.html)