Teaching const

[News system]

In article <786 at srs.UUCP> srs!craig at cs.rochester.edu (Craig Schmackpfeffer) writes:
>In article <9683 at ism780c.UUCP> marv at ism780.UUCP (Marvin Rubenstein) writes:
>>In article <27071 at amdahl.uts.amdahl.com> nw at amdahl.uts.amdahl.com (Neal Weidenhofer) writes:
>>>	int * const a;
>>>decodes as:
>>>	a is a constant,
>>>	a is a constant pointer,
>>>	a is a constant pointer to an int.
>>>		(i.e., a cannot be modified but *a can.)
>>
>>Note that:
>>	 int a[1];
>>decodes as:
>>       a is a constant,
>>       a is a constant pointer,
>>       a is a constant pointer to an int.
>>	       (i.e., a cannot be modified but *a can.)
>>
>>But there must (?) be some difference between the two.  How do you teach
>>this?
>>
>
>Of course there is a difference!  The "int * const a" declaration declares 
>a pointer to an int.  The "int a[1]" declaration ALLOCATES space for an 
>int and "a" itself is not a pointer, but actually the location of the array.
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
But "a" itself a pointer or else *a would not be allowed.  Nor would:

     char p = a;

I wrote the >> article.  I should have used a smiley.  I was discussing the
*teaching* problem.  Have you ever tried to explain to a novice why:

  char *p; and char p[1];

mean the same when p is a parameter, but do mean the same when p is not
a parameter.  Or why:

    extern  char p[];

makes sense, but

      char p[];

is an error.  If your students don't have any problems with this then they
are much smarter than mine (smiley used this time :-).

       Marv Rubinstein -- Interactive Systems