public string Save(ClassRoom classRoom)
 {
     if (classRoomGateway.CheckSlot(classRoom) && classRoomGateway.CheckSlot2(classRoom))
     {
         return("Slot already Booked");
     }
     else
     {
         if (classRoomGateway.Save(classRoom) > 0)
         {
             return("Saved");
         }
         else
         {
             return("Not saved");
         }
     }
 }