I highly recommend
Richard Buckland's Higher Computing Course. It's not technically a course in C, but it's an intro course and they use C so they teach along the way as needed. It effectively functions as a nice intro to C.
But I recommend it not just for the C but for general programming concept stuff as well. They explore a bunch of cool stuff: looking at how transistors work one day, then using dummy machine code another day, exploring how the stack works and the mechanics behind function calls, etc, etc, etc.
But the big reason I mention it is the guy Richard is just a great teacher, a joy to watch. If you have any interest/appreciation for the process of teaching and learning, I recommend watching just to see how he functions. He reminds me of Casey in that they both have this infectious enthusiasm for the subject matter and just for learning in general. Watching both Casey and Richard, you learn
so much more than the course content. You are infused with this spirit and energy and whole entire philosophy to programming and to life. It's wonderful, if you like handmade hero, I recommend it.
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I'm not sure how actually deep into C they get as I've sadly never completely finished the whole series, I usually peter out around the halfway point (it's something like 50 hours of lectures, and I like to do the assignments along with the class, [whee look at me, little phantom student]). Actually, I've attempted to finish a few times over the years, each time coming back like I would to an old favorite TV show, binge watching as much as I can one weekend, hacking away at some sudoku solver in the back ground.. it's great fun. (But each time, life happens; I get derailed. Don't let that deter you though, give it a shot anyway!)
If you only watch one, I guess I'd recommend the one I discovered the series through when it got sent around a long while back,
"Everything you need to know about pointers."
Since it's just the recorded videos of an actual class that took place back in 08 or whenever, it can meander a bit and sometimes you get some meta stuff related to it being at an actual university with actual students, plus there is some padding/waiting at the edge of the lectures... But for me that flavor is like the super icing on the cake. It really gives me this sweet nostalgic feeling like I'm really back in college. I wish I had CS classes this good back then!