It all started with an idea, something to scratch a personal itch. I was learning elementary French, and realized that there is an algorithmic approach to generating the numbers. Not a very elegant algorithm, but one that could easily be turned into a computer program.
The idea turned into a function, and soon enough it turned into an iPhone app, now called Les Nombres and available from the App Store (and also for Windows Phone). My function takes a nonnegative integer and turns it into a French language string, which is displayed on the screen. It could be fed into a speech synthesizer, but in Les Nombres the numbers are recordings of a native French speaker, which I think is nice. (And I couldn’t use recordings of Apple’s “Virginie” voice from OS X anyway due to its license.)
To keep things simple, Les Nombres only deals with the numbers 0 to 100, even though my function could do up to 1,000 out of the box. It involves some 90 lines of Objective-C code, including two recursive calls. It was fun to write, and I learned something in the process, but ultimately I didn’t have to write it at all.