Where are the c header files on my system?

[Lori Nagel]

I've been using gcc in Linux and cc in Unix. 
I have not been using an IDE, only the terminal shell and a text
editing program for the C files. On both computers c programs compile
and run, however, the compilers are different and have different options,
and some code that compiles and runs on one doesn't on the other.  (what I mean is why is gcc so lax while cc is so mean.) 

What
I want to know is if there any easy way I could find out where my .h
files are  on my computers such as stdio.h? Also, would I be able to
find the function prototypes for things  like scanf in them or would I
have to go somewhere else? 

Another thing, why oh why did they decide to seperate out libm.a from the rest of the C programming libriaries so that you have to include it? It used to make me so upset until I read intro to gcc. 

Please someone answer my question
because I have been wanting to know the answer for about 3 years now,
and I think that is a long enough time to wait.  I have done enough reading of manuals to know that most of them don't answer the questions that people have. I'm planning to write the ultimate newbie C programming book for Gnu/Linux because it doesn't currently exist.