A mobile app developer always gets some of the stuff out from the running techniques.
Someone who have worked solely with the App developers knows that they are the people who juggle with the new ideas.
These canny & talented peoples adopt lots of high quality coding tutorials, books, and overall resources on the web.
Without further ado, lets dive in...
Udemy is by far the most popular place to learn to code in my opinion.
Exercism has tons of exercises in most programming languages.