def classes_for_day(day)
      days_classes = ClassArray.new
      self.each { |c| days_classes << c if c.day == day }
      days_classes.count > 0 ? days_classes : nil
    end
def classes_for_day(day)
      days_classes = ClassArray.new
      self.each { |c| days_classes << c if c.day == day }
      days_classes.count > 0 ? days_classes : nil
    end
Returns an array of all the classes for the day