I would do both, but prioritize learning by doing. For theory, focus on what is commonly tested in interviews, namely algorithms and data structures. I would a

I would do both, but prioritize learning by doing. For theory, focus on what is commonly tested in interviews, namely algorithms and data structures. I would also suggest auditing an online course on operating systems. That shouldn't take much effort (compared to actually doing the associated homework etc), but gives context, a good overview of a lot of fundamental concepts, and probably enough CS trivia to be useful in an interview. Once you have a job, then I'd focus on learning theory. You'll be learning by doing all day in the job, so there's less benefit from side projects than continuing to learn theory, at least until you've covered everything in the undergrad curriculum. You can look at the degree requirements from a couple of the big schools, choose a list of topics, then pick one or two sources for each topic. I used a mix of online courses and textbooks.