Header Files

myprog.h:
  
extern int sum(int, int);

extern int mode;
 
main.c: sum.c:
  
#include "myprog.h"

int mode;

int main(void)
{
    int x = sum(11, 22);
}

#include "myprog.h"

int sum(int a, int b)
{
    int r = a + b;
    return r;
}