I believe the latter is just a later, expanded edition of the former. I do know that they are all part of a series that he has been revising for two decades, s

I believe the latter is just a later, expanded edition of the former. I do know that they are all part of a series that he has been revising for two decades, starting with "Algorithms" which was in Pascal, then branching out to have editions in C and Modula-3, then revisions in several volumes/parts. The first edition of Algorithms in C was just a single volume. The paperback you mention is probably just a copy of that edition - if I'm looking at the same one as you, it looks like a paperback of the hardcover I remember from fifteen years or so ago.