Full-text books available for download with authors' permissions
"Learn C The Hard Way will fill in the "beginning programmer" gap in the literature on the C Programming language. It will teach good modern C programming practices and avoid habits that lead to buffer overflows, security defects, and other problems that even experienced programmers cause."
Github repo for this course: https://github.com/paulgribble/CBootCamp.git
"Stanford CS Education Library: A 45 page summary of the C language. The coverage is pretty quick, so it is most appropriate as review or for someone with some programming background in another language. Topics include variables, int types, floating point types, promotion, truncation, operators, control structures (if, while, for), functions, value parameters, reference parameters, structs, pointers, arrays, the preprocessor, and the standard C library functions."
The online version of The C Book, second edition by Mike Banahan, Declan Brady and Mark Doran, originally published by Addison Wesley in 1991.