#include <stdio.h>

/* The following explicit declaration of variable a as extern
   tells the compiler to look for the declaration of this variable
   elsewhere on the same file above this place or on other files

   gcc -ansi -c a*.c    => a1.o, a2.o
   gcc -ansi a*.o -o a	=> a
   The order of object files for the link command has no significance
*/
extern int a, b, c;  /* variables a, b, c  are declared as external */

int b; /* global variable b - can be accesed from any file */
int c = 8;

main()
{
  extern int c, d;
  a = 15;
  b = 20;
  printf(" a = %d\n b = %d\n c = %d\n d = %d\n", a, b, c, d);
}