Note, and you may know, but none of the sites you list are C++ reference sites. They are code challenge sites that do not teach C++, they do nothing more than provide a set of problems to solve that exercises what you already know. They are also notorious for providing poor code, and in many cases, just flat dangerous boiler-plate code due to lack of validation for you to use as a beginning for the challenges. (for challenge sites teaching C++ isn't the goal, solving a specific challenge is). Yes, you will learn various new algorithms and techniques to solve specific problems, which could be written in any language, just don't confuse that with learning proper C++.Also, while exploring some C++ resources online like C++ forums and sites such as Udemy, Coursera, Hackerrank, Codeacademy and Pass4Future ...
The primary "reference" for C++ on the internet is cppreference.com. Make sure you understand the distinction between a language reference and a challenge site. Otherwise you will likely pick up poor coding practices that are difficult to unlearn later. StackOverflow is littered with questions from challenge sites.
Good luck with your coding, and I concur, no quirks regarding I/O.
Statistics: Posted by drankinatty — Sat Oct 18, 2025 4:43 am