If you want to write applications for iOS or macOS, you will want to start with this book. Based on our legendary training, Objective-C: The Big Nerd Ranch Guide covers C, Objective-C and common programming idioms that will help you make the most of Apple technologies.
Prior to purchasing this guide, I had tried a couple books and online training at Udemy. None of them come close to the Big Nerd Ranch book in effectiveness. This book is very good for both absolute beginners and those experienced in object-oriented programming. The text is clear and to the point and you get plenty, plenty of practice. That's where Big Nerd Ranch books set themselves apart.
Richard Yates on Amazon