Thought I'd also have a go at translating ch-1.pl and ch-2a.pl into C..

Both C versions produce near-identical (non-debugging and even debugging)
output to the Perl originals.

The C translation of ch-2a.pl was quite hard to write, mainly on storage
allocation, to minimise that I changed it to a per-list callback
(from building a list of paths)

They use most of my regular support modules:
- a command-line argument processing module args.[ch],
- a csvlist-of-int parsing module parseints.[ch], and
- an int-array printing module printarray.[ch].