From: Josef 'Jupp' SCHUGT <jupp@...>
Date: 2004-02-28T10:07:53+09:00
Subject: Arabic # -> Roman # (Was: TDD Roman Numeral tutorial in Ruby)

Hi!

Wrote a simple conversion tool. Takes one command line argument. 
Interpretes it as a decimal number. Prints roman number for it. 
Returns 1 on error, 0 on success. Conversion of single digits has two 
cases

a) digit is 4 or 9. In this case append n1[i] followed by n5[i] if
   digit is 4 and by n1[i+1] if digit is 9.

b) digit is neither 4 nor 9. In this case append n5[i] if digit is 
   greater or equals 5. Then append d modulo 5 times n1[i].

As far as tables are concerned uses bare necessities - symbols need
to be stored in any case. Converting tool to a function is left as an
exercise :->

The algorithm is not new. It is a formal representation of what one
does when manually writing roman numbers. It can easily be expanded
to additional symbols by simply adding them to the lists.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

#!/usr/bin/env ruby

n1 = [ 'I', 'X', 'C', 'M' ]
n5 = [ 'V', 'L', 'D', nil ]

max = 0

n1.each_index { |i| max += 3 * 10 ** i }
n5.each_index { |i| max += 5 * 10 ** i unless i.nil? }

exit 1 if ARGV.length != 1

x = ARGV.first.to_i
r = ""

exit 1 if x > max or x < 1

(n5.length - 1).downto(0) { |i|
  d  = x / 10 ** i
  x -= d * 10 ** i
  if d == 4 or d == 9
    r << n1[i] + (d == 4 ? n5[i] : n1[i+1])
  else
    if d >= 5
      r << n5[i]
      d -= 5
    end
    r << n1[i] * (d % 5)
  end
}

puts r
exit 0

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Didn't find a simpler solution. Improvements are welcome.

Josef 'Jupp' SCHUGT
-- 
E-Mail: .--- ..- .--. .--. .--.-. --. -- -..- .-.-.- -.. .
http://oss.erdfunkstelle.de/ruby/    -     German comp.lang.ruby FAQ
http://rubyforge.org/users/jupp/     -     Ruby projects at Rubyforge