Attacking an open-source software to promote another open-source software. You needed to do better dear Eclipse Foundation. This isn't the philosophy behind open-source.
edit:
Wait. Is this an early April fools' day joke?
Essential parts of C language are actually really a small set.
What I'd suggest is, learn syntax and try to understand linux kernel (which is one of the very well crafted software piece we have written in C). If you don't want to go that much of a deep dive, you can check sqlite source code as well. Writing code starts with reading it. Do yourself a favour and spend more time on reading code than reading books.