chap_08_c.rb

=begin

Expand upon englishNumber some more. Now put in millions, so you get 'one
million' instead of 'one thousand thousand'. Then try adding billions and
trillions. How high can you go?

=end

def englishNumber number
  if number < 0  # No negative numbers.
    return 'Please enter a number that isn\'t negative.'
  end
  if number == 0
    return 'zero'
  end

  # No more special cases! No more returns!

  numString = ''  # This is the string we will return.

  onesPlace = ['one',     'two',       'three',    'four',     'five',
               'six',     'seven',     'eight',    'nine']
  tensPlace = ['ten',     'twenty',    'thirty',   'forty',    'fifty',
               'sixty',   'seventy',   'eighty',   'ninety']
  teenagers = ['eleven',  'twelve',    'thirteen', 'fourteen', 'fifteen',
               'sixteen', 'seventeen', 'eighteen', 'nineteen']

  # "left" is how much of the number we still have left to write out.
  # "write" is the part we are writing out right now.
  # write and left... get it?  :)

  left  = number

  #quadrillions
  write = left/1000000000000000
  left  = left - write*1000000000000000

  if write > 0
    quadrillions  = englishNumber write
    numString = numString + quadrillions + ' quadrillion'

    if left > 0
      numString = numString + ' '
    end
  end

  #trillions
  write = left/1000000000000
  left  = left - write*1000000000000

  if write > 0
    trillions  = englishNumber write
    numString = numString + trillions + ' trillion'

    if left > 0
      numString = numString + ' '
    end
  end

  #billions
  write = left/1000000000
  left  = left - write*1000000000

  if write > 0
    billions  = englishNumber write
    numString = numString + billions + ' billion'

    if left > 0
      numString = numString + ' '
    end
  end

  #millions
  write = left/1000000
  left  = left - write*1000000

  if write > 0
    millions  = englishNumber write
    numString = numString + millions + ' million'

    if left > 0
      numString = numString + ' '
    end
  end

  #thousands
  write = left/1000
  left  = left - write*1000

  if write > 0
    thousands  = englishNumber write
    numString = numString + thousands + ' thousand'

    if left > 0
      numString = numString + ' '
    end
  end

  write = left/100          # How many hundreds left to write out?
  left  = left - write*100  # Subtract off those hundreds.

  if write > 0
    # Now here's a really sly trick:
    hundreds  = englishNumber write
    numString = numString + hundreds + ' hundred'
    # That's called "recursion". So what did I just do?
    # I told this method to call itself, but with "write" instead of
    # "number". Remember that "write" is (at the moment) the number of
    # hundreds we have to write out. After we add "hundreds" to
    # "numString", we add the string ' hundred' after it.
    # So, for example, if we originally called englishNumber with
    # 1999 (so "number" = 1999), then at this point "write" would
    # be 19, and "left" would be 99. The laziest thing to do at this
    # point is to have englishNumber write out the 'nineteen' for us,
    # then we write out ' hundred', and then the rest of
    # englishNumber writes out 'ninety-nine'.

    if left > 0
      # So we don't write 'two hundredfifty-one'...
      numString = numString + ' '
    end
  end

  write = left/10          # How many tens left to write out?
  left  = left - write*10  # Subtract off those tens.

  if write > 0
    if ((write == 1) and (left > 0))
      # Since we can't write "tenty-two" instead of "twelve",
      # we have to make a special exception for these.
      numString = numString + teenagers[left-1]
      # The "-1" is because teenagers[3] is 'fourteen', not 'thirteen'.

      # Since we took care of the digit in the ones place already,
      # we have nothing left to write.
      left = 0
    else
      numString = numString + tensPlace[write-1]
      # The "-1" is because tensPlace[3] is 'forty', not 'thirty'.
    end

    if left > 0
      # So we don't write 'sixtyfour'...
      numString = numString + '-'
    end
  end

  write = left  # How many ones left to write out?
  left  = 0     # Subtract off those ones.

  if write > 0
    numString = numString + onesPlace[write-1]
    # The "-1" is because onesPlace[3] is 'four', not 'three'.
  end

  # Now we just return "numString"...
  numString
end

puts englishNumber(  0)
puts englishNumber(  9)
puts englishNumber( 10)
puts englishNumber( 11)
puts englishNumber( 17)
puts englishNumber( 32)
puts englishNumber( 88)
puts englishNumber( 99)
puts englishNumber(100)
puts englishNumber(101)
puts englishNumber(234)
puts englishNumber(3211)
puts englishNumber(999999)
puts englishNumber(1000000000000)
puts ''
puts englishNumber(1000)
puts englishNumber(1000000)
puts englishNumber(1000000000)
puts englishNumber(1000000000000)
puts englishNumber(1000000000000000)