The C Programming Language, second edition, is the canonical beginner book.
The C Book, available for free at
http://publications.gbdirect.co.uk/c_book/, is also a good starting point. These books cover the version of C that was standardized in 1989, known as
C89 or
C90. Though C89 is over 20 years old, it is still the most relevant version of C today and is widely supported by C compilers. The current version of C was standardized in 1999 and is known as
C99. I'm not aware of any books that cover C99, nor is C99 widely supported by compilers.