家有小虎

using System.Globalization;
GregorianCalendar gc = new GregorianCalendar();
int weekOfYear = gc.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstDay, DayOfWeek.Monday);

using System.Globalization;
/// <summary>
/// 获取某一日期是该年中的第几周
/// </summary>
/// <param name="dt">日期</param>
/// <returns>该日期在该年中的周数</returns>
private int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
return gc.GetWeekOfYear(dt, CalendarWeekRule.FirstDay, DayOfWeek.Monday);
}

using System.Globalization;
/// <summary>
/// 获取某一年有多少周
/// </summary>
/// <param name="year">年份</param>
/// <returns>该年周数</returns>
private int GetWeekAmount(int year)
{
DateTime end = new DateTime(year, 12, 31);  //该年最后一天
System.Globalization.GregorianCalendar gc = new GregorianCalendar();
return gc.GetWeekOfYear(end, CalendarWeekRule.FirstDay, DayOfWeek.Monday);  //该年星期数
}