E21 Answer

8 

Comments: There is a single external entity that corresponds to the idenfifier x. Both files file21A.c and file21C.c refer to that one entity. The linker "knows" to create just one variable x, which is initialized to 8.

When foo() is called, it sets its local variable x to 99, but this is a different entity than the external variable x, which is unique.

/* --- file21A.c --- */
int x = 8



/* --- file21B.c --- */
foo()
{
  int x;
  x = 99;
}



/* --- file21B.c --- */
int x;
main()
{
  foo();
  printf("%d\n", x );
  system("pause"); 
}