Re: ada loops

[Dave Thompson <david.thompson1@worldnet.att.net>]

On 30 May 2003 13:25:31 -0400, Stephen Leake <Stephe.Leake@nasa.gov>
wrote:
[for variable local to loop]
> I don't remember how Pascal did this; I suspect the loop variable was
> not a new declaration. In standard C++, the loop variable is a new
> declaration (as in Ada), but in early versions of C++, it wasn't.
> 
Not exactly.  In C++ you have an explicit choice:

1) if you write e.g. for( i = 0; i < 10; i++ ) ... it uses an existing
variable (which must be) already available (declared).

2) if you write e.g. for( int i = 0; i < 10; i++ ) ... it creates a
new variable.  But what happens thereafter varies:  

2A) in pre-standard C++ (aka ARM) this declaration remains in scope 
(and the variable valid) after the loop, to the end of the containing
{ } block -- so you can't declare another variable (or anything) with
the same name, in particular you can't do another for ( int i = 0 ...;

2B) in standard C++(88) it is declared and exists only to the end of
the loop.

In all cases, you need to match the type of the loop variable to the
range of values assigned; this isn't determined for you automatically,
nor checked for overflow (in practice, theoretically it's allowed).

C99, BTW, adds to C the 2B variant.


- David.Thompson1 at worldnet.att.net