Hello @glv
I’ve been meaning to post about the Nyhoff book on the forum as I’m a fan of what the authors have done. At first, the book seemed deceptively simple and even repetitive at times. But, as I worked my way through it became apparent their goal to lay a solid foundation for students who have little to zero background in code of any kind is superbly executed. They provide a macro view of programming concepts and best practices and use processing as the vehicle to explain. Other books I have used appear to take the opposite tack of primarily teaching processing and overall concepts of programming follow. (***Disclaimer alert! 
Please note, I appreciate the existence of both approaches and do not believe one is better than the other.)
Specifically “what the code is doing under the hood” re this book:
Every explanation of function covered is basically diagrammed so that the *novice coder can visualize where the math and logic happen and how the code flows from line to line.
For me, this book a hidden gem. I have yet to see any other posts about it and may write a more thorough user experience at some point.
But hopefully, in the meantime, this adds some clarity to my experience with their book as a teaching/learning resource.
*novice coder = zip, zero, nada programming; OR a bit of experience but still unsure what or why unexpected results for certain code solutions.