#include <stdio.h>

/* int a = 9;
   This second global declaration of the same variable a
   causes the link error: multiple declaration of a
*/

/* extern int a = 9;
   It is invalid to (default) initialize a variable that
   has been declared elsewhere
*/

extern int a;

void f1(void)
{
  extern b;
  printf("\nFrom f1:  a = %d  b = %d\n", a, b);
}