1  extern int printf (const char *,...);
       2  
       3  struct s { struct s *n; } *p;
       4  struct s ss;
       5  #define MAX     10
       6  struct s sss[MAX];
       7  int count = 0;
       8  
       9  void sub( struct s *p, struct s **pp );
      10  int look( struct s *p, struct s **pp );
      11  
      12  main()
      13  {
      14      struct s *pp;
      15      struct s *next;
      16      int i;
      17  
      18      p = &ss;
      19      next = p;
      20      for ( i = 0; i < MAX; i++ ) {
      21          next->n = &sss[i];
      22          next = next->n;
      23      }
      24      next->n = 0;
      25  
      26      sub( p, &pp );
      27      if (count != MAX+2)
      28        abort ();
      29  
      30      exit( 0 );
      31  }
      32  
      33  void sub( struct s *p, struct s **pp )
      34  {
      35     for ( ; look( p, pp ); ) {
      36          if ( p )
      37              p = p->n;
      38          else
      39              break;
      40     }
      41  }
      42  
      43  int look( struct s *p, struct s **pp )
      44  {
      45      for ( ; p; p = p->n )
      46          ;
      47      *pp = p;
      48      count++;
      49      return( 1 );
      50  }