gistfile1.rb

class Magic
  @@a = 0
  def initialize(attack_point,defence_point)
    @attack_point = attack_point
    @defence_point = defence_point
  end

  def level_up
    @@a += 1
    @attack_point * (1 + @@a) 
  end

  def attack
    @attack_point
  end

  def defence_point
    @defence_point
  end
end

nanoha = Magic.new(10,5)
#fate = Magic.new(8,4)

p nanoha.level_up
p nanoha.attack
# nanoha.level_up
#p nanoha.attack
# nanoha.level_up
#p nanoha.attack
# nanoha.level_up
#p nanoha.attack