The only thing you need to have in adt.h is prototypes for the
functions declared in adt.c

/* Apple Disk Transfer 1.22

adt.h: declarations for routines in adt.c
*/

static void print_help(char *name);
void send_directory();
void send_disk();
void send_sector( unsigned char *buffer, int part, int track, int
sector );

void receive_disk();
void receive_sector( unsigned char *buffer, int part, int track, int
sector );

void getfname( char *fname );
void comm_puts( char *p );

void make_crctable();
unsigned short do_crc( unsigned char *ptr, int count );