North West Ruby User Group

NWRUG Quiz: Roman Numerals Kata

The Romans were a clever bunch. They conquered most of Europe and ruled it for hundreds of years. They invented concrete and straight roads amongst other things. One thing they never discovered though was the number zero. This made writing and dating extensive histories of their exploits slightly more challenging, but the system of numbers they came up with is still in use today. For example the BBC uses Roman numerals to date their programmes.

The Romans wrote numbers using letters - I, V, X, L, C, D, M. (notice these letters have lots of straight lines and are hence easy to hack into stone tablets)

For this Kata, you are going to write a some code that convert the Hindu-Arabic numbers we use into Roman Numerals. For example,

 1 becomes I
 10 becomes X
 7 becomes VII

For a full description of how Roman Numerals works, see this useful reference website.

There is no need to be able to convert numbers larger than about 3000. (The Romans themselves didn't tend to go any higher)

Stretch Goal

If you finish the challenge and want a further one, try and write some code that does the reverse conversion, converting a Roman Numeral to an Hindu–Arabic number system.


  • Can you make the code really beautiful and highly readable?
  • Does it help to break out lots of small named functions from the main function, or is it better to keep it all in one function?
  • If you don't know an algorithm to do this already, can you derive one using strict TDD?
  • Does the order you take the tests in affect the final design of your algorithm?
  • Would it be better to work out an algorithm first before starting with TDD?
  • If you do know an algorithm already, can you implement it using strict TDD?
  • Can you think of another algorithm?
  • what are the best data structures for storing all the numeral letters? (I, V, D, M etc)