README.md

NumberToPhrase

Simple ruby script to convert numbers to phrases. This serves as example script to teach basics of ruby.

number_to_phrase.rb

class NumberToPhrase
  DIGIT_WORDS =
    %w(zero
       one
       two
       three
       four
       five
       six
       seven
       eight
       nine
       ten
       eleven
       twelve
       thirteen
       fourteen
       fifteen
       sixteen
       seventeen
       eighteen
       nineteen).freeze

  TENS_WORDS =
    %w(ten
       twenty
       thirty
       forty
       fifty
       sixty
       seventy
       eighty
       ninety).freeze

  POSITION_WORDS = [nil, 'thousand', 'million', 'billion', 'trillion'].freeze

  attr_reader :num

  def initialize(num)
    @num = num
  end

  def convert
    return 'zero' if num.zero?

    group_by_position(num).collect do |(group, place)|
      number_part = group.reverse.join('').to_i

      next unless number_part > 0
      phrase_part = _num_to_phrase(number_part)

      [phrase_part, place]
    end.flatten.compact.join ' '
  end

  def to_s
    convert
  end

  def self.[](num)
    new(num).to_s
  end

  private

  def group_by_position(num)
    num
      .digits
      .each_slice(3)
      .zip(POSITION_WORDS)
      .reverse
  end

  def _num_to_phrase(num)
    if num < 20
      DIGIT_WORDS[num]
    elsif num < 100
      convert_tens(num)
    else
      convert_hundreds(num)
    end
  end

  def convert_tens(num)
    [TENS_WORDS[num / 10 - 1],
     convert_remainder(num % 10)]
  end

  def convert_hundreds(num)
    [
      "#{_num_to_phrase(num / 100)} hundred",
      convert_remainder(num % 100)
    ]
  end

  def convert_remainder(remainder)
    _num_to_phrase(remainder) if remainder > 0
  end
end

number_to_phrase_test.rb

require_relative 'number_to_phrase'
require 'minitest/autorun'

class NumberToPhraseTest < Minitest::Test
  def test_zero
    assert_equal 'zero', NumberToPhrase.new(0).to_s
  end

  def test_one
    assert_equal 'one', NumberToPhrase.new(1).to_s
  end

  def test_8
    assert_equal 'eight', NumberToPhrase.new(8).to_s
  end

  def test_ten
    assert_equal 'ten', NumberToPhrase.new(10).to_s
  end

  def test_18
    assert_equal 'eighteen', NumberToPhrase.new(18).to_s
  end

  def test_78
    assert_equal 'seventy eight', NumberToPhrase.new(78).to_s
  end

  def test_99
    assert_equal 'ninety nine', NumberToPhrase.new(99).to_s
  end

  def test_100
    assert_equal 'one hundred one', NumberToPhrase.new(101).to_s
  end

  def test_112
    assert_equal 'one hundred twelve', NumberToPhrase.new(112).to_s
  end

  def test_219
    assert_equal 'two hundred nineteen', NumberToPhrase.new(219).to_s
  end

  def test_515
    assert_equal 'five hundred fifteen', NumberToPhrase.new(515).to_s
  end

  def test_999
    assert_equal 'nine hundred ninety nine', NumberToPhrase.new(999).to_s
  end

  def test_919
    assert_equal 'nine hundred nineteen', NumberToPhrase.new(919).to_s
  end

  def test_145
    assert_equal 'one hundred forty five', NumberToPhrase.new(145).to_s
  end

  def test_1101
    assert_equal 'one thousand one hundred one', NumberToPhrase.new(1101).to_s
  end

  def test_34101
    assert_equal 'thirty four thousand one hundred one', NumberToPhrase.new(34_101).to_s
  end

  def test_134101
    assert_equal 'one hundred thirty four thousand one hundred one', NumberToPhrase.new(134_101).to_s
  end

  def test_100000
    assert_equal 'one hundred thousand', NumberToPhrase.new(100_000).to_s
  end

  def test_speed_of_light
    assert_equal 'two hundred ninety nine million seven hundred ninety two thousand four hundred fifty eight', NumberToPhrase.new(299_792_458).to_s
  end

  def test_square_brackets
    assert_equal 'eight', NumberToPhrase[8]
  end
end