ListItem add_data = new ListItem();
DateTime xxx;
xxx = (DateTime)(DateTime.Now);
while (xxx > DateTime.Now.AddDays(-10)){
     add_data.Value = "#" + xxx.ToShortDateString() + " 0.00.00#";
      add_data.Text = xxx.ToShortDateString();
       DropDownList4.Items.Add(add_data);
       DropDownList1.Items.Add(add_data);
       xxx = xxx.AddDays(-1);
}