I don't have Horton's book, but two chapters in an evening is a fast pace for any technical book! I don't know if his book as questions/exercises at the end of each chapter... I prefer books that do, so I can tell if I'm really learning the stuff. You wrote 7 programs based on the first 2 chapters, so clearly you're ready for chapter 3 !
In general, tutorial-style books re-use and build-upon previous chapters as you advance through the book. You'll know when you're moving too fast when you have to go back and re-study something.
Do NOT try to memorize everything (unless you have a photographic memory).There is a LOT to C++ ! The more you practice, the less you'll have to look-up, but all programmers use reference books.
