Actually, according to this very enlightening read (http://eternallyconfuzzled.com/arts/jsw_art_rand.aspx), you're all wrong...

(sorry, I couldn't help it either) :mrgreen:

I don't think you even need Top3 (and you're using it uninitialized, which is bad). Top will be updated as you call pop, so you could probably just do:
while(Top)
pop(Top);

I tried running it and after a few small touchups (no logical changes though) it seems that you're off to a good start. Here's how it went:
$ ./a.out
this is a line

enil a si siht As you can...

You'll need a bignum library. I've seen mention of the Gnu Multiple Precision (http://gmplib.org/) library before, so you might give that a shot.

Instead of giving a book answer, I figured I'd help you help yourself: did you try it? You can learn a lot just from experimenting and seeing if something works or not.

Actually, my brain wasn't really functioning either, now that I look at it. The no-brainer algorithm we all jumped on works so long as the coins are multiples of each other, or have a fairly high...

To summarize the algorithm provided by Lazarus, you just add as many of the biggest coin you can. Then repeat for the next biggest until you have the amount.