class.h
=======
#define   CLASS_SIZE   100

struct student {
   char   *last_name;
   int    student_id;
   char   grade;
};

class.c
=======
#include   "class_info.h"

int fail(struct student class[])  /* Count the failing grades. */
{
   int   i, cnt = 0;
   for (i = 0; i < CLASS_SIZE; ++i)
      cnt += class[i].grade == 'F';
   return cnt;
}


complex.h
=========
struct complex {
   double   re;      /* real part */
   double   im;      /* imag part */
};
typedef   struct complex   complex;

complex.c
=========
#include   "complex.h"

void add(complex *a, complex *b, complex *c)   /* a = b + c */
{
   a -> re = b -> re + c -> re;
   a -> im = b -> im + c -> im;
}