/* go_or_back.c */

unsigned _mark;
void mark()
{
  int dummy;
  _mark = *(unsigned *)(&dummy + 2); // 2‚͊‹«‚Ɉˑ¶
}

unsigned _target;
void jump()
{
  int dummy;
  unsigned *p_ret_addr = (unsigned *)(&dummy + 2);
  *p_ret_addr = _target;
}

main()
{
  int c = 3;
  unsigned first, second;

  printf("Enter main.\n");
  mark();
  first = _mark;
  printf("first: c = %d\n", c);
  mark();
  second = _mark;
  printf("second: c = %d\n", c);

  c--;
  printf("\ngo or back? c = %d\n\n", c);
  switch (c) {
  case 2:
    _target = first;
    jump();
    break;
  case 1:
    _target = second;
    jump();
    break;
  default:
    ;
  }
  printf("Leave main. c = %d\n", c);
}