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HACKING: The art of exploitation - great programming book in general
(repo.zenk-security.com)
A subreddit dedicated to the C language with an emphasis on microcontrollers and low level hardware. However, all C discussion welcome :)
Related communities:
I usually like microcontroller tutorials for learning C, as pointers are a bit more real, and there's not really any dynamic memory to confuse people about.
But yeah, I could see it as a good resource to learn