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;
}
}