help with Ada question

help with Ada question

[pa.dec.com!nntpd2.cxo.dec.com!shodha!wallace]

wallace@shodha (Richard Wallace) writes:
: rwalker@barnacle.micro.umn.edu (robert walker) writes:
: : 
: : If neither an exit nor a goto statement were available for Ada, how
: : might you simulate the action of an exit statement?
: : 
: 
: The following is one of may ways to control loop itteration without the
: exit and goto verbs.  Note that I've only shown monotonicly increasing
: loop control.
: 
: You would have to introduce a guard action on the loop control statement and
: use an if to control skipping statements thus:
: 

It seems I wiped-out the other half of my emacs buffer!  Sorry!  I'll
reconstruct the code fragment again.

code fragment:

help with Ada question

[pa.dec.com!nntpd2.cxo.dec.com!shodha!wallace]

wallace@shodha (Richard Wallace) writes:
: wallace@shodha (Richard Wallace) writes:
: : rwalker@barnacle.micro.umn.edu (robert walker) writes:
: : : 
: : : If neither an exit nor a goto statement were available for Ada, how
: : : might you simulate the action of an exit statement?
: : : 
: : 
: : The following is one of may ways to control loop itteration without the
: : exit and goto verbs.  Note that I've only shown monotonicly increasing
: : loop control.
: : 
: : You would have to introduce a guard action on the loop control statement an
d
: : use an if to control skipping statements thus:
: : 
: 
: It seems I wiped-out the other half of my emacs buffer!  Sorry!  I'll
: reconstruct the code fragment again.
: 
: code fragment:
: 

It seems my mailer is having problems...  I saved this file out and what got
posted is truncated.  Hmm...  I'll try ONE more time.

LOOP_COUNTER := 1;
LOOP_EXIT    := false;

MAIN_LOOP:

while ( not( LOOP_EXIT) and ( LOOP_COUNTER <= LOOP_MAXIMUM ) ) then

	{do statements}

	if {boolean clause} then
		LOOP_EXIT := true; -- setup for a psudeo exit
	end if;

	if not( LOOP_EXIT ) then -- psuedo exit statment in this guard.
		{do statements if guard is true, i.e. no exit statement}
	end if;

	LOOP_COUNTER := LOOP_COUNTER + 1;

end loop MAIN_LOOP;

This is one of many solutions.  I hope this helps.  Note that this is a
monotonically incrementing loop.  To do the reverse clause you'd have to
count down.  To change the increment you'd have to change the constant 1
in the LOOP_COUNTER assignment.

Aloha,
	Richard

--------------

Richard Wallace
Senior Software Engineer
Digital Equipment Corporation
301 Rockrimmon Blvd. South
CXO2-1/7A
Colorado Springs, CO 80919-2398
(719)548-2792
<wallace@cookie.enet.dec.com>

"The opinions expresses are my own, B.P. may not *quite* agree..."

Re: help with Ada question

[Paul Schwartz]

robert walker (rwalker@barnacle.micro.umn.edu) wrote:
: 
: I could use some help on an Ada question. I have a homework problem
: which states:
: 
: 
: If neither an exit nor a goto statement were available for Ada, how
: might you simulate the action of an exit statement?
: 
: 
: This is for a course in higher level languages. We are studying control
: structures of several languages. I have never programmed
: in Ada, and am new to the language.
: 
: Thanks for any help in advance.
: 
: Robert Walker
: rwalker@mermaid.micro.umn.edu
: 
: 
	The easiest way would be to put the loop in a block and use an
EXCEPTION to get out of the loop.  As in;
fooLoop:
BEGIN
	LOOP
		IF <condition> THEN
		RAISE Some_Error;
		END IF;

       stuff
	END LOOP;
	EXCEPTION 
	WHEN Some_Error => NULL; --you just wanted out of the loop
END fooLoop;

--
>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<
Paul Schwartz       pschwrtz@lynx.cs.washington.edu

Re: help with Ada question

[portal!cup.portal.com!R_Tim_Coslet]

In article: <1992Nov1.090527.29814@beaver.cs.washington.edu>
	pschwrtz@lynx.cs.washington.edu (Paul Schwartz) wrote:
>robert walker (rwalker@barnacle.micro.umn.edu) wrote:
>: 
>: If neither an exit nor a goto statement were available for Ada, how
>: might you simulate the action of an exit statement?
>: 
>	The easiest way would be to put the loop in a block and use an
>EXCEPTION to get out of the loop.  As in;
>fooLoop:
>BEGIN
>	LOOP
>		IF <condition> THEN
>		RAISE Some_Error;
>		END IF;
>
>       stuff
>	END LOOP;
>	EXCEPTION 
>	WHEN Some_Error => NULL; --you just wanted out of the loop
>END fooLoop;
>
It may be EASY, but don't EVER use exceptions as a "normal" means of
exiting a loop!!!! The overhead of an exception may be significant and
this is a misuse of the feature!!!

This is fine, IFF the exit from the loop was because of an error condition
that would normally never occur.

Of course this is purely a "class assignment" question, as any real programming
rules would never prohibit use of exit statements!

                                        R. Tim Coslet

Usenet: R_Tim_Coslet@cup.portal.com
        technology, n.  domesticated natural phenomena