gistfile1.rb

class Magic
  @@magical_girls = 0
  def initialize(attack_point,defence_point)
    @attack_point = attack_point
    @defence_point = defence_point
    @@magical_girls += 1
  end

  def attack
    @attack_point
  end

  def defence
    @defence_point
  end

  def ribbon=(color)
    @@ribbon = color
  end

  def ribbon
    @@ribbon
  end

  def self.girls
    @@magical_girls
  end

  def level_up
    @attack_point *=2
    @defence_point *= 2
  end
end


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

puts nanoha.attack
puts nanoha.defence
puts fate.attack
puts fate.defence
nanoha.level_up
fate.level_up
puts nanoha.attack
puts nanoha.defence
puts fate.attack
puts fate.defence
nanoha.level_up
fate.level_up
puts nanoha.attack
puts nanoha.defence
puts fate.attack
puts fate.defence

#nanoha.ribbon = "white"
#puts nanoha.ribbon
#puts fate.ribbon
#puts Magic.girls

ちょっと違う。
level_upさせるごとに元の攻撃力の2倍、3倍と増えていって欲しいんだ。

なのはさんだと
nanoha.attack
=> 10
nanoha.level_up
nanoha.attack
=> 20
nanoha.level_up
nanoha.attack
=> 30

みたいな感じ。