获取一年中某周的起始和截止日期，获取一年有多少周

/// <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>
        private void GetWeek(int nYear, int nNumWeek, out   DateTime dtWeekStart, out   DateTime dtWeekeEnd)
        {
            DateTime dt = new DateTime(nYear, 1, 1);
            dt = dt + new TimeSpan((nNumWeek - 1) * 7, 0, 0, 0);
            dtWeekStart = dt.AddDays(-(int)dt.DayOfWeek + (int)DayOfWeek.Monday);
            dtWeekeEnd = dt.AddDays((int)DayOfWeek.Saturday - (int)dt.DayOfWeek + 1);
        }

/// <summary>
        /// 求某年有多少周
        /// 返回 int
        /// </summary>
        /// <param name="strYear"></param>
        /// <returns>int</returns>
        private int GetYearWeekCount(int strYear)
        {
            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 == 1)
            {
                int countDay = fDt.AddYears(1).AddDays(-1).DayOfYear;
                int countWeek = countDay / 7 + 1;
                return countWeek;
            }
            else
            {
                int countDay = fDt.AddYears(1).AddDays(-1).DayOfYear;
                int countWeek = countDay / 7 + 2;
                return countWeek;
            }
        }