20011223-1.c

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

/* Origin: Joseph Myers <[e-mail]>.  */
/* Case labels in a switch statement are converted to the promoted
   type of the controlling expression, not an unpromoted version.
   Reported as PR c/2454 by
   Andreas Krakowczyk <[e-mail]>.  */

extern void exit (int);
extern void abort (void);

static int i;

int
main (void)
{
  i = -1;
  switch ((signed char) i) {
  case 255:
    abort ();
  default:
    exit (0);
  }
}