When comparing Beej's Guide to Network Programming vs SoloLearn, the Slant community recommends SoloLearn for most people. In the question“What are the best resources to learn C/C++?” SoloLearn is ranked 3rd while Beej's Guide to Network Programming is ranked 21st.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Free
Available for free online and as a pdf.
Pro Completely free
Pro Offline learning mode for mobile apps
Allows learning while disconnected from the net.
Pro Easy for beginners
Anyone can get started with this.
Pro Share and modify others' projects
Pro Browser-based code playgrounds
No software installation needed, just a modern web browser. On mobile devices though the mobile apps are highly recommended.
Pro Excellent mobile apps available
Pro Gamification
XP, levels, badges, certificates, etc.
Cons
Con Only the most commonly used languages are covered.
C++, Java, JavaScript, C#, Python, SQL, PHP, Swift, Ruby, JQuery, HTML, CSS. You won't find anything less common like Haskell, Erlang, Elixir, Common Lisp, Scheme, Clojure, Rust, etc.
Con Limited usefulness for intermediate or experienced programmers
No advanced coding challenges. Look for those on other sites like hackerrank.