List<FlightInfo> List = Schema.getFlightinfo();
             FlightInfo flightinfo = new FlightInfo();
             Iterator search = List.iterator();
             while(search.hasNext()) {
              flightinfo = (FlightInfo) search.next();
              if (flightinfo.getFlightID() == (FlightId))
              {
                  flightinfo.setAvailableSeats(flightinfo.getAvailableSeats() - Available_Seats);
                  BookSeats = flightinfo;
              }
             }