Some information for the one who decided to learn C++, and now wants to learn at least a bit of C?

Some time ago I decided to learn C++, and most of the documentation I
found (books, tutorials, etc) said that not only is it not necessary
to learn C before, it is not recommended since it could make things
more difficult.

Now I know C++, but I deal a lot with various C software, and although
I understand it all, it is not at all easy to adapt it to my needs.

Where should I search for information? I couldn't find anything useful
on Google (and it's not that easy to find a good search query).

Could you advise me? Any responses are welcome.