** Start of listing of h.c **
#include <stdio.h>

int main(void) {
  printf("Content-type: text/plain;charset=us-ascii\n\n");
  printf("hello, world\n");
  return 0;
}
** End of listing of h.c **

Here is the directory entry for that source file:
-rw-------  1 rem  user  138 Feb 28  2007 h.c
   ^ Note user execute permission *not* needed for source files.

That gets compiled to a.out, but then renamed to something.cgi
so that it will be usable by remote users via CGI:
-rwx------  1 rem  user  4415 Feb 28  2007 h-c.cgi
   ^ Note user execute permission needed for all CGI programs.
(because compiled-C is native machine code run directly on machine)