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- The C Book: available for free online
This is a good resource to help you start learning C. It is a little out of date with some of the modern features as it was publish in 1991 prior to the C99 or C11 standards but nonetheless it is a good place to start. Also it teaches by complete example which is a big plus. - The GNU C Tutorial:available for free here
Given that the GNU foundation is responsible for GCC the most commonly used C compiler it makes sense that they have an excellent language tutorial. However unlike The C Book, examples are provided as snippets not complete examples which may make learning a bit more disjointed. If you are confused about a specific concept or feature it is a great place to look. - C Reference Card:
Not a tutorial per-se but it is a good tool to have available, especially when you are just getting started.
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