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

Both C versions produce identical (non-debugging) output to my Perl originals

ch-1.c uses primes.[ch], a prime number generator module that I wrote ages ago.

ch-2-slow.c was my original implementation of the ch02.pl in C, but it was
hopelessly slow - The only tricky issue is how to represent the seen set.
Here I went for the obvious bitmap approach, but initializing the seen bitmap
in ishappy() takes a long time.

ch-2.c is the tweaked version which stores the seen set as a "dynamically
growable bitmap", this is very much faster than ch-2-slow.c