protected void Mark_Present(object sender, CommandEventArgs e)
{
string course_id = Request.QueryString["val1"];
string sectionid = Request.QueryString["val2"];
int index = Convert.ToInt32(e.CommandArgument);
// Retrieve the row that contains the button
// from the Rows collection.
GridViewRow row = Students.Rows[index];
string roll_no = row.Cells[0].Text;
objBL.Mark_Present(roll_no, course_id, sectionid);
}