调试易

string[] a=new string[3]
a[1]=DateTime.Now
a[2]=DateTime.Now.AddDays(-7);
a[3]=DateTime.Now.AddDays(-14);int不能存日期

还要转化一下。DateTime.Now.AddDays(-7).ToString();

            DateTime d = getMonday();
            MessageBox.Show("本周一日期为：" + d.Date.ToString());
            MessageBox.Show("上周一日期为：" + d.AddDays(-7).Date.ToString());
            MessageBox.Show("上上周一日期为：" + d.AddDays(-14).Date.ToString());        protected DateTime getMonday()
        {
            DateTime d = DateTime.Now;
            switch (d.DayOfWeek)
            {
                default: return d.Date;
                case DayOfWeek.Tuesday: return d.AddDays(-1).Date;
                case DayOfWeek.Wednesday: return d.AddDays(-2).Date;
                case DayOfWeek.Thursday: return d.AddDays(-3).Date;
                case DayOfWeek.Friday: return d.AddDays(-4).Date;
                case DayOfWeek.Saturday: return d.AddDays(-5).Date;
                case DayOfWeek.Sunday: return d.AddDays(-6).Date;
            }
        }这个答案是不是你要的呢？

如果说不用数据库的话这样就OK了
如果是要得到数据库的
sql="select * from table where datediff(week,riqi,getdate())<=2" //得到近两周的
--查询本周
select * from table where create_day>=dateadd(day,2-datepart(weekday,getdate()),convert(varchar,getdate(),112))
 and create_day<dateadd(day,9-datepart(weekday,getdate()),convert(varchar,getdate(),112))--上周
select * from table where create_day>=dateadd(day,-5-datepart(weekday,getdate()),convert(varchar,getdate(),112))
 and create_day<dateadd(day,2-datepart(weekday,getdate()),convert(varchar,getdate(),112))

 IList<DateTime> lst = new List<DateTime>();
            DateTime dt1 = DateTime.Now;
            DateTime dt2 = DateTime.Now.AddDays(-7);
            DateTime dt3 = DateTime.Now.AddDays(-14);