CousinRoman

CousinRoman provides functionality to convert between Roman and Arabian numerals. The functionality provided via String and Integer extensions.

Roman numbers and conversion rules

CousinRoman follows strict roman notation with subtractive rule, i.e.

1. Letters should be ordered by decreasing of magnitude.
2. Only I, X, C, M can be repeated, but up to three times.
3. Letter with lower magnitude can appear BEFORE letter with higher magnitude, but only in the following cases: IV, IX, XL, XC, CD, CM - lets call them subtractives
4. subtractives and regular letters cannot appear within the same power, i.e. ivi is not allowed.

Therefore, only numbers within range of 1..3999 can be represented in roman notation.

CousinRoman is thoroughly spec'ed, and considered reliable in following these rules.

Installation

Add this line to your application's Gemfile:

gem 'cousin_roman'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cousin_roman

Usage

Just use String#to_arabian or String#to_arabian! methods if you want to convert from Roman to Arabian and Integer#to_roman or Integer#to_roman! if you want to convert from Arabian to Roman.

For example:

'MMXIII'.to_arabian # => 2013
'MMYUOX'.to_arabian # => nil
'MMYOUX'.to_arabian! # => TypeError: not a valid roman number

2013.to_roman # => 'MMXIII'
'0'.to_roman # => nil
'100500'.to_roman! # => TypeError: not a valid roman number

String#to_arabian(!) is case insensitive.

Integer#to_roman(!) returns numerals in upper case.

Testing

Just run

$ rake

under gem folder (be prepared for massive output).

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request