// Public symbols from main.c
// These are just declarations; the definitions are in main.c
extern unsigned char data Sec, Min, Hr, Day;

// Public symbols from calc.c
// These are just declarations; the definitions are in calc.c
extern unsigned char code Zero [] = {0x03, 0x61, 0x11, 0x03};
extern unsigned int Value = 0;
extern unsigned char dat;

#include "main.h" // Declarations only
#include "calc.h" // Declarations only

// Now provide the definitions of the public symbols for main:
// It doesn't matter that the declarations have been included;
// in fact, including the declarations means that the compiler will spot any inconsistencies!
unsigned char data Sec, Min, Hr, Day; 

#include "main.h" // Declarations only
#include "calc.h" // Declarations only

// Now provide the definitions of the public symbols for calc:
unsigned char code Zero [] = {0x03, 0x61, 0x11, 0x03};
unsigned int Value = 0;
unsigned char dat;