There are many good books about the C language, and these are among the best:

• Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, Second Edition Prentice Hall, Inc., 1988. This book was co-authored by the original language designer and is regarded by many to be the authoritative reference on C.
• K. N. King, C Programming: A Modern Approach (Second Edition) W. W. Norton & Company, 2008. This examples-based book includes best practices in using the language most effectively.
• Steve Oualline, Practical C Programming, Third Edition O'Reilly Media, 1997. This introductory C book follows the no-nonsense, practical approach common to Nutshell Handbooks(R).

Once you have learned enough about the C language, you may wish to extend your knowledge to the C++ language. The Texas Advanced Computing Center (TACC) hosts an archive of course materials from their online class C++ for C programmers. This course was presented in February and October 2018. The class teaches idiomatic C++ to C programmers and focuses on two aspects of the language. It first explains object-oriented programming and then discusses the C++ mechanisms, especially for parameter passing and memory management, that improve on the mechanisms provided by C.