A good beginning tutorial
These spanish guys have it all, tutorials, book recomendations and all sorts of links, very good resource.
But beware about C and searching for help on it, when people say they are C
experts then they mean what we call ANSI C, now that is just basic
C and has nothing to do with how to communicate with the operating system
that the program is supposed to be run on so beware when you ask for help on
C programming that you know isnt ANSI C compatible, it is most of the time
better to ask someone who is expert on that particular subject.
There are several addons to C that you need to know off, I wont go into the windows addons since I know nothing about them.
First there is the GTK+ toolkit that gives a nice look to your application.
Ncurses can create a nice layout on your xterm or console.
There is also a good reference to ncurses in The Linux Programming Guide chapter 8.
Motif is not really popular, but some people like it.
While your learning C be expected to hear some people say "This is not the correct way to do it!". There are a lot of ways to program in C, some ways are dependent on the compiler you use and some things you can just do in several ways. So while your learning C be prepared for more experienced programmmers to say something like that, as long as it works its ok, but you might run into situations where one way of coding works but another doesnt so it is a good thing to practice "Correct programming" as defined by the ANSI standard from the beginning.
The way to learn ANSI C is to buy the book by Kernighan and Ritchie, The C Programming Language, it is called the C bible since they are the authors of the language (Ritchie is also one of the authors of the Unix system). If you read that one from page 1 to end then you should be very comfortable in the C language.