What are convincing examples where pointer arithmetic is preferable to array subscripting?

Question

I\'m preparing some slides for an introductory C class, and I\'m trying to present good examples (and motivation) for using pointer arithmetic over array subscripting.

Answer 1

#include ctype.h
void skip_spaces( const char **ppsz )
{
  const char *psz = *ppsz;
  while( isspace(*psz) )
    psz++;
  *ppsz = psz;
}

void fn(void)
{
  char a[]="  Hello World!";
  const char *psz = a;
  skip_spaces( &psz );
  printf("\n%s", psz);
}