I'm a programmer who usually uses C++, but I'm about to start doing iphone and android programming for some freelance gigs. I was wondering what are some good books to leaning objective-c and iphone development in general? I've read some articles on the differences between c and objective-c and find that there aren't too many, but I would love to have just a good informative book to reference. And I'll like to get savvy with the ios SDK. I played around with it, but I learn best through practical examples.

To be honest there are no really good go to books for objective-C in the same way that there are standard books that everybody uses for other languages.

For example Java, C++, and Javascript all have a book in the Effective series (Effective C++, Effective Javascript etc..) which most proffesional programmers in these languages will swear by and have been written by well known experts in the field. However the Effective Objective C book is very poorly researched and written and is full of bugs, errata and misinformation (just check the errata section on the books github page).

The other thing to remember is that every year at WWDC Apple will update the language and compiler with new features (ARC, Blocks, GCD, No more synthesizing, no need to forward declare methods, boxed literals are just a few of the features I can think of that have been changed in the last 3 to 4 years) this means any book you buy will get outdate pretty quickly.

If you want to learn to write an iOS app then just pick up the latest "Beggining IOS <insert OS number here> Programming". Then when you want to get a bit deaper with Objective C you should watch all the language presentations from at least the past 3 years WWDCs.

What I do if I have a new topic to learn is subscribe to http://www.safaribooksonline.com/ for as long as I need to get up to speed. It gives you a libray of books instead of committing to just one. I have found this the fastest and likely the cheapest option.