protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                //default trip type if user do not select anything
                Session["tripType"] = "One Way";

                GetFlightDetails getFlightDetails = new GetFlightDetails();

                //bind distinct sources to drop down source
                listSource.DataSource = getFlightDetails.GetSource();
                listSource.DataBind();

                //bind distinct travel class to drop down
                listClass.DataSource = getFlightDetails.GetClass();
                listClass.DataBind();
            }


            //disabling dates before current day
            txtDateOfJourney.Attributes["min"] = DateTime.Now.ToString("yyyy-MM-dd");
            txtDateOfReturn.Attributes["min"]  = DateTime.Now.ToString("yyyy-MM-dd");

            DropDownList1_SelectedIndexChanged(sender, e);
        }