How to make a validation in 5.2?

Please can any one give a idea about this type validation.

public function joinclass()
{
  if($class_code = $request->get('class_code');
    $classroom = classroomModel::where('class_code',$class_code)->first();
    var_dump($classroom->toArray());)
   {
      $class = new joinclass();
    $class -> user_id = Auth::user()->id;
    $class -> class_code = $request['class_code'];
    $class -> save();
   }else{
     Flash::message('Your code is not found in databse');
    }
}