ranking.rb

class Ranking
  attr_reader :rankings, :current_rank
  def initialize
    @rankings = [-8, -7, -6, -5, -4, -3, -2, -1, 1, 2, 3, 4, 5, 6, 7, 8]
    @rank_index = 0
    @current_rank = rankings[@rank_index]
  end

  def up
    return "Already at highest rank" if @rank_index == 15 
    @current_rank = rankings[@rank_index += 1]
  end

  def down
    return "Already at lowest rank" if @rank_index == 0
    @current_rank = rankings[@rank_index -= 1]
  end
end

Simplified Version

class Ranking
def initialize
@current_rank = -8
end

def up
return "Already highest Rank" if @current_rank == 8
@current_rank == -1 ? @current_rank += 2 : @current_rank += 1
end

def down
return "At lowest Rank" if @current_rank == -8
@current_rank == 1 ? @current_rank -= 2 : @current_rank -= 1
end

def current
@current_rank
end
end