--- to_i
--- to_i(base)          ruby 1.7 feature

    ʸ 10 ʿɽȲᤷơѴޤ

        p " 10".to_i    # => 10
        p "010".to_i    # => 10
        p "-010".to_i   # => -10

    ȤߤʤʤʸФޤǤѴоݤȤޤѴоݤ
    ʸǤ 0 ֤ޤ

        p "0x11".to_i   # => 0

    hex, oct, to_f, 
    Integer, Float 
    ⻲ȤƤ

    դˡͤʸѴˤ 
    sprintf,
    %,
    Integer#to_s [Integer/to_s]
    Ѥޤ

    ruby 1.7 feature:
    ꤹ뤳ȤǥǥեȤ 10 ʰʳ 2  36 ʿؤѴ
    ԤȤǤޤޤ0 ꤹ prefix ˤȽ
    ޤ(դ prefix ǧΤ 0 ꤷȤǤ)
    0, 2  36 ʳΰꤷ硢㳰 ArgumentError ȯ
    ޤ

        p "0b10".to_i(0)  # => 2
        p "0o10".to_i(0)  # => 8
        p "010".to_i(0)   # => 8
        p "0d10".to_i(0)  # => 10
        p "0x10".to_i(0)  # => 16

