how to add items to the dropdown inside gridview and how to bind it

       //inside rowdatabound of gridview find the dropdown and bind it like below

  DropDownList ddlQuantity = e.Row.FindControl("ddlQuantity");
     // now you have a ddl
     //{ write a method here to bind the ddl }



       // write this into the selectedindex_change of ddlQuantity

 Control ddlQuantity = (DropDownList)sender as Control;
 GridViewRow gvRow = ddlQuantity.NamingContainer as GridViewRow;

       //now you have the current row of the grid where the dropdown is
       // lets the dropdown selected value is 2 then

Label price =   (Label)gvReplyAdded.Rows[gvRow.RowIndex].FindControl("lblPrice");
Label Amount = (Label)gvReplyAdded.Rows[gvRow.RowIndex].FindControl("lblAmount");
Amount.Text = (Convert.ToInt32(price.Text) * Convert.ToInt32(((DropDownList)sender).SelectedValue)).ToString();

     //here you can get the control of gridview of the same row

<itemtemplate>
<asp:dropdownlist runat="server" id="ddl" width="100%" datatextfield="FieldName" datavaluefield="FieldValue" appenddatabounditems="true" datasourceid="SqlDataSource1" xmlns:asp="#unknown">

<asp:listitem text="" value="0" selected="True" />
                                        </asp:dropdownlist>
                                        <asp:hiddenfield runat="server" value="<%# Bind("FieldId") %>" id="DDL1" xmlns:asp="#unknown" /> 
</itemtemplate>

<asp:SqlDataSource ID="SqlDataSource1" SelectCommandType="StoredProcedure" SelectCommand="usp_Name"
                    runat="server">
                    <SelectParameters>
                        <asp:Parameter Name="ParamName" DefaultValue="0" />
                    </SelectParameters>
                </asp:SqlDataSource>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {

        if (e.Row.RowType == DataControlRowType.DataRow)
        {
           DropDownList ddl = ((DropDownList)e.Row.FindControl("ddl"));
            HiddenField hdn = ((HiddenField)e.Row.FindControl("DDL1"));
  	    ddl.SelectedValue =	hdn.value
        }
}