C Primer. It's thick, but it has lots of info. A very good reference book.
But if you're too lazy (like me 😉 ) and/or you have no idea about C/C++, SAMS Teach Yourself C in 24 Hours by Tony Yang is a great book. The author explains many very basic details that usually overlooked by other authors, for example, he explains why/what is "#include <stdio.h>" for 2.5 pages (p 31-33). However, the author doesn't cover in-depth and highly technical stuff.