Valid pointer operations in C

Pointers of same type can be assigned and can be assigned to and
from generic pointer type (void *).  All other assignments require a cast and
are machine dependent and dubious.

Pointer + integer and Pointer - integer are valid as long as the pointer
is within the range of the same array; the pointer can also go one beyond 
the upper end of an array as long as no attempt is made to access the value 
pointed to.

Pointer to entries of the same array can be subtracted giving an
integer and can be compared using ==, <=, etc.  
Pointers can be compared to NULL.

The contents can be evaluated, that is *pointer is valid, as long as the 
pointer is not NULL or of type void * and has been initialized (via address 
operator &, assignment or an alloc type function).