class Hundred
  def initialize(difficulty)
    @difficulty = difficulty
    @correct = 0
    @error   = 0
  end

  def question
    case @difficulty
    when 1
      "%d %c %d = " % [rand(10),  [:+, :-, :*].choice, rand(10)].
        tap {|a, op, b| @ans = a.send(op, b) }
    when 2
      "%d %c %d = " % [rand(100),  [:+, :-, :*, :/].choice, rand(100)].
        tap do |a, op, b|
          unless b == 0 || a < b || a % b != 0
            @ans = a.send(op, b)
          else
            retry
          end
        end
    end
  end

  def answer(ans)
    if ans == @ans
      @correct += 1
      '正解'
    else
      @error += 1
      '不正解'
    end
  end

  def result(start)
    "正解　：#{@correct}\n" +
    "不正解：#{@error}\n" +
    "時間　：#{Time.now - start} sec"
  end

end

if $0 == __FILE__
  puts '計算 100 開始'
  print '難易度を選択してください。1:かんたん 2:むずかしい > '
  difficulty = gets.chomp.to_i
  case difficulty
  when 1
    print '1:かんたんを開始します'
  when 2
    print '2:むずかしいを開始します'
  else
    puts '1か２を選択してください'
    exit 1
  end
  print ' plese enter > '
  gets

  h = Hundred.new difficulty

  start = Time.now
  100.times do |i|
    print h.question
    puts h.answer gets.chomp.to_i
    puts

    if (i+1) % 10 == 0
      puts "#{i+1}問突破"
      puts
    end
  end

  puts h.result start
end