The rules that MUST be followed:
--------------------------------

1- Make our code fit in 80 columns unless it's not practical to do so
because of a long function name or an expression that would become
unreadable if broken on several lines.

2- NO TABS... set your editor to produce spaces instead of tabs...
that's because some editors use 4 chars tabs and some use 8 chars and
everything looks screwed up if you allow the use of tab chars.

#1 and #2 are also a requirement with some of our external clients.

3- Brackets... we use this
     if (...)
     {
         ...;
     }
     else
     {
         ...;
     }

More flexible rules: (some may not apply depending on context)
--------------------

4- Indent is 4 chars usually.  We've used 2 chars in some places but we
try to stick to 4.

5- Use hungarian notation for variables (makes more sense in C than in
PHP):

 Prefix     Description
 ------     ----------------------------
   b         Boolean
   c         Char
   n         Integer value
   i         Integer, used as a counter in a loop for instance
             (we also often use the vars i, j, or k for counters)
   f         Float, single precision
   d         Double precision Float (we also use "df" sometimes)
   sz        String zero-terminated (a C string!)
   by        Byte
   o         Object
   s         Structure
   fp        FILE *

   a         Array of ...
   p         Pointer to ...
   
   k         Constant
   m         Class member variable (we also use "m_" sometimes)
   g         Global variable

 Examples:
 ---------
   char   szFilename[100];
   char   *pszFilename;
   int    nProjectId;
   int    i, j, k;
   int    iField;
   double dX, dY;
   char   **papszLines;
   TABFile *poSrcFile;
   GBool  bSuccess;


6- Function and variable names use upper-lowercase combinations instead
of underscores, e.g.  int nProjectId instead of project_id,

7- Filenames and directory names: 

    - Avoid spaces or special non-alphanumerical characters in filenames.
      The safe characters to use in filenames are "a-z", "0-9", "_" and "."

    - Avoid uppercases in filenames, except for special files that should
      show up at the top of a directory listing like README.TXT, 
      INSTALL.TXT, etc.  For the rest try to stick to lowercase-only 
      filenames, that makes our lives much easier when porting code 
      between Windows and Unix.

8- Comments... quite flexible... we most of the time use something like
this for function headers:

/*****************************************************************
 *                          MyFunction()
 *
 * This function will do something pretty cool.  It expects numbers
 * as arguments and returns a pointer to a buffer newly allocated.
 *
 * The caller should free the returned buffer.  NULL is returned in
 * case of error.
 *****************************************************************/

and for comments inline, it's either a short one-line /*... */ thing, or
if it's longer then we sometimes use the following to also act as a
delimiter of an important part of a function:

/* --------------------------------------------------------------
 *  OK, this is an interesting comment...
 * -------------------------------------------------------------- */

Some people (Frank and Assefa at least) use some Emacs macros 
to automatically format these comments.