fill gird according to Dropdown Selected iteam

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C#

ASP.NET

in a form there are two drop down list they filled with month name, i use this code to fill the fill drop down list ..in page load..

if (!IsPostBack)
         {
              for (int i = 4; i >=1; i--)
              {
                  string Month = (Convert.ToDateTime("01/" + i.ToString("00") +"/"+ DateTime.Now.Date.ToString("yyyy"))).ToString("MMM");
                  ddlFromMonth.Items.Insert(0, new ListItem(Month,i.ToString()));
              }
              FillToMonth();

And second dropdown filles with this code

private void FillToMonth()
       {
           ddlToMonth.Items.Clear();
           for (int i = Convert.ToInt32(ddlFromMonth.SelectedValue)+5; i >= Convert.ToInt32(ddlFromMonth.SelectedValue); i--)
           {
               string Month = (Convert.ToDateTime("01/" + i.ToString("00") + "/" + DateTime.Now.Date.ToString("yyyy"))).ToString("MMM");
               ddlToMonth.Items.Insert(0, new ListItem(Month, i.ToString()));
           }

how i fill girdview according to January to march, April to june, july to sep, oct to Dec.while we choose value in drop down list