/// <summary>  /// 获得今年有几周  /// </summary>  /// <param name="year"></param>  /// <returns></returns>   public int GetWeekOfYear(int year)   {        DateTime the_Date = new DateTime(year,1,1);//本年的第一天         TimeSpan tt=the_Date.AddYears(1)-the_Date;//求出本年有几天         return tt.Days / 7 + 1; //因为年只有366天和365天除以7有余数所以始终需要加一周   }

   DateTime dt = new DateTime(2007, 1, 1);    //在.net中内部处理是减去+1后的月份得到当前月的天数(实际上这种方式是算出他们的差)例如:    //当前月是2007年1月1日,通过AddMonths方法加一个月是2007年2月1日,在.net中将算出它们间隔多少天.    //所以我们可以利用这种方法来求出当前月有几天     TimeSpan tt = dt.AddMonths(1) - dt;    // DateTime dt = new DateTime(2007,1,31); 如果时间是2007,1,31加一个月减当前月就不行,看下面解释:    /*比如说给你做一个项目，2010-01-01给你做的，一个月做完，就是2010-02-01交付     现在2010-01-31号给你做，也是要求一个月做完，本来是应该在2010-02-31号交付的，但是2月没有31号，所以交付的时间就变成2010-02-28号了     AddMonths只是增加一个月的时间*/     Response.Write(tt);

public static int year;     public static int month;     public static int days;     protected void Button1_Click(object sender, EventArgs e)     {         year = DateTime.Now.Year;         month = DateTime.Now.Month;         //得到当前月的天数         switch (month)         {             case 1:                 days = 31;                 break;             case 2:                 if (DateTime.IsLeapYear(year))                 {                     //闰年二月为29天                     days = 29;                 }                 else                 {                     //不是闰年，二月为28天                     days = 28;                 }                 break;             case 3:                 days = 31;                 break;             case 4:                 days = 30;                 break;             case 5:                 days = 31;                 break;             case 6:                 days = 30;                 break;             case 7:                 days = 31;                 break;             case 8:                 days = 31;                 break;             case 9:                 days = 30;                 break;             case 10:                 days = 31;                 break;             case 11:                 days = 30;                 break;             case 12:                 days = 31;                 break;         }         TextBox1.Text = days.ToString();     }

protected void Page_Load(object sender, EventArgs e)         {             int day=GetWeekDay(2010,11);             if (day != 0)             {                 Response.Write(day);             }         }         public int GetWeekDay(int year,int month)         {             switch (month)             {                 case 1:                 case 3:                 case 5:                 case 7:                 case 8:                 case 10:                 case 12:                     return 31;                 case 2:                     if (DateTime.IsLeapYear(year))                         return 29;                     else                         return 28;                 case 4:                 case 6:                 case 9:                 case 11:                     return 30;                 default:                     return 0;                 }