Do I need to learn C to learn from the online version of the red book? Because all I know is C++. One more question, does the publised Red Book use C++?

You''ll probably be fine. I mean, the syntax is the same, there may just be some C standard library functions that aren''t used much in C++ that you aren''t familiar with. But since the book is online and won''t cost you anything, why not just try it and find out?

The latest print version of the Red Book is straight C.