Algorithm that converts numeric amount into English words

Question

What is the most efficient way to convert numeric amount into English words

e.g. 12 to twelve 127 to one hundred twenty-seven

Answer 1

Start by solving 1-99, using a list of numbers for 1-20, and then 30, 40, ..., 90. Then add hundreds to get 1-999. Then use that routine to give the number of each power of 1,000 for as high as you want to go (I think the highest standard nomenclature is for decillion, which is 10^33).

One slight caveat is that it's a little tricky to get the blanks right in all cases if you're trying to start and end without an excess blank. The easy solution is to put a blank after every word, and then strip off the trailing blank when you're all done. If you try to be more precise while building the string, you're likely to end up with missing blanks or excess blanks.