During CS 152, we have introduced a few different ways to compile.  Here, we'll
summarize them and tell what they mean.

If all of your code is in one file, called myprogram.c,
clang myprogram.c

that will create an executable named a.out

If you want to name your executable something different, say, myprogram

clang -o myprogram myprogram.c

Maybe you want to call it mywackyprogram

clang -o mywackyprogram myprogram.c

Okay, so now you've got this awful bug.  It has a segmentation fault or an 
infinite loop, and you want to figure out where that is happening and be 
able to inspect the variable values.  You need to compile it with extra
information for gdb

clang myprogram.c -g

The -g flag tells it to put in debugging information for a debugger.
Now you can use gdb

gdb a.out

Information on gdb is in another file.

Okay, what if you have your code spread among different files?  You might
have your main in facebook.c, then a bunch of functions implemented in 
friend.h / friend.c, friends.h / friends.c, link.h / link.c, etc.

You have two choices - compile everything separately and link together at the
end, or compile everything together.

You should be compiling one file as you finish it just to search for 
small errors, though you won't be able to test it until you have the main.

To compile a single file that is only a subset of the program:

clang -c link.c

This will compile link.c and produce a file called link.o
You can do this with all of the individual .c files.

Then, at the end, do this:

clang facebook.o friend.o friends.o link.o  .....

You can also combine this with what you learned above

clang -o facebook facebook.o friend.o friends.o link.o ...