this is a gcc file, you can download it and learn its usetility, for further detail please look at t

				f()				{				  int x = 1;				#if defined(STACK_SIZE)				  char big[STACK_SIZE/2];				#else				  char big[0x1000];				#endif								  ({				    __label__ mylabel;				  mylabel:				    x++;				    if (x != 3)				      goto mylabel;				  });				  exit(0);				}								main()				{				  f();				}