.Net时间计算函数，统计某一天是一年的第几周，这一周从哪天开始到哪天结束

/// <summary>

/// 计算某年第一周的天数

/// </summary>

/// <param name="dt">某年中的一个时间</param>

/// <returns></returns>

public static int DaysInFirstweekInYear(DateTime dt)

{

DateTime FirstDate = Convert.ToDateTime(string.Format("{0}-1-1", dt.Year));

int DayOfWeekInYear = DayOfWeek(FirstDate);

int DaysInFirstWeek = 8 - DayOfWeekInYear;

return DaysInFirstWeek;

}

/// <summary>

/// 一年中的第几周

/// </summary>

/// <param name="dt"></param>

/// <returns></returns>

public static int WeekOfYear(DateTime dt)

{

int days = DaysInFirstweekInYear(dt);

int dayofyear = dt.DayOfYear;

if (dayofyear < days) return 1;

else

{

int week2 = (int)Math.Ceiling((double)(dayofyear - days) / (double)7);

return week2 + 1;

}

}

/// <summary>

/// 传入某一天，输出这一周的起始日期

/// </summary>

/// <param name="dt"></param>

/// <returns></returns>

public static DateTime[] DatesIncludeDay(DateTime dt)

{

DateTime[] dts = new DateTime[2];

int dayofweek = DayOfWeek(dt);

dts[0] = dt.AddDays(1 - dayofweek);

dts[1] = dt.AddDays(7 - dayofweek);

return dts;

}

/// <summary>

/// 计算星期几，转换为数字

/// </summary>

/// <param name="dt">某天的日期</param>

/// <returns></returns>

public static int DayOfWeek(DateTime dt)

{

string strDayOfWeek = dt.DayOfWeek.ToString().ToLower();

int intDayOfWeek = 0;

switch (strDayOfWeek)

{

case "monday":

intDayOfWeek = 1;

break;

case "tuesday":

intDayOfWeek = 2;

break;

case "wednesday":

intDayOfWeek = 3;

break;

case "thursday":

intDayOfWeek = 4;

break;

case "friday":

intDayOfWeek = 5;

break;

case "saturday":

intDayOfWeek = 6;

break;

case "sunday":

intDayOfWeek = 7;

break;

}

return intDayOfWeek;

}

调用：

DateTime dt = Convert.ToDateTime("2013-1-6");
Dictionary<string, DateTime> dict = new Dictionary<string, DateTime>();
dict.Add("0001", DateTime.Now.AddDays(-100));
dict.Add("0002", DateTime.Now.AddDays(-99));
dict.Add("0003", DateTime.Now.AddDays(-98));
dict.Add("0004", DateTime.Now.AddDays(-97));
dict.Add("0005", DateTime.Now.AddDays(-96));
dict.Add("0006", DateTime.Now.AddDays(-95));
dict.Add("0007", DateTime.Now.AddDays(-94));
dict.Add("0008", DateTime.Now.AddDays(-93));
dict.Add("0009", DateTime.Now.AddDays(-92));
dict.Add("0010", DateTime.Now.AddDays(-91));
dict.Add("0011", DateTime.Now.AddDays(-90));
dict.Add("0012", DateTime.Now.AddDays(-89));
dict.Add("0013", DateTime.Now.AddDays(-88));
dict.Add("0014", DateTime.Now.AddDays(-87));
dict.Add("0015", DateTime.Now.AddDays(-86));
dict.Add("0016", DateTime.Now.AddDays(-85));
dict.Add("0017", DateTime.Now.AddDays(0));
dict.Add("0018", DateTime.Now.AddDays(1));
dict.Add("0019", DateTime.Now.AddDays(2));
string str = "";
foreach(KeyValuePair<string,DateTime> kv in dict)
{
DateTime[] dts = Common.OperateText.DatesIncludeDay(kv.Value);
str = str + string.Format("{0},第{1}周,时间{2:yyyy-MM-dd},本周从{3:yyyy-MM-dd}到{4:yyyy-MM-dd} <br/>",kv.Key,Common.OperateText.WeekOfYear(kv.Value),kv.Value,dts[0],dts[1]);
}

Response.Write(str);

效果：