E23 Answer

99 

Comments: There is just one object x, which is referred to in all three files. The object x is initialized to 8, but then the call to foo() changes it to 99.

/* --- fileA.c --- */
int x = 8;



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



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