Coding doesn’t have to be hard work all the time, it can be a recreational activity as well. Here’s a site I enjoy going back to now and then, when ideas for personal projects have run out, or I just want a tough challenge.
Project Euler is a collection of math based coding challenges, where you can submit and verify your result, when you’ve found a solution.
I’m still a rookie on the site, but I have solved quite a few problems. Here’s my badge and a challenge to beat my score!
Another site that focuses on honing your skills is http://codewars.com. It’s a novel puzzle site, with a martial arts theme, so leveling up means advancing your Kyū through the various colours and gaining honor. It’s less mathematically inclined than Project Euler and so, somewhat more approachable.
Referral for Honor.
http://exercism.io/ is more similar to codewars, but without all the theming and rewards stuff and just shows your progress. It has a nice command-line client for handling submissions and both automated and human feedback on each submission.