I presumed that the book would still be useful for my iMac with OS X 10.5, but I have found it very tough going. There are enough differences between what the book describes and shows that I spend more time trying to figure out the 10.5 version of their 10.4 instructions than actually learning how to program. That I am just beginning to learn how to program, my difficulty might reflect more about me than the book. I also perhaps should have taken as a hint that if Wrox hasn't come out with a 10.5 version of this book, there might be a reason for it. The book seemed impressive enough that I though it worth a try. I regret buying the book since I doubt that I will really be able to use or benefit from it. I will soon try 'Learn C on the Mac' by Dave Marks, published by Apress to see if that works better for me. Lesson learned: don't buy computer books for versions other than what you have.