Re: Exit Loop_Statement

Re: Exit Loop_Statement

[Robert Dewar]

In article <39182781.C1780175@bton.ac.uk>,
  John English <je@bton.ac.uk> wrote:
> Just before Robert roasts me again, let me point out that my
talking
> about Constraint_Error was due misremembering the original
code as
> involving an assignment Clients(1..3) := "Stop". I've just
revisited
> the code and now I'm going to go and wipe the egg off my face.


Right, and that's why I thought the hint "will this ever be
true?" was an appropriate one :-)


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Before you buy.

Re: Exit Loop_Statement

[DuckE]

"David Freshwater" <dafresh@odyssey.apana.org.au> wrote in message
news:39181473@news.wa.apana.org.au...
> Hi,
>    Thanks for the help....I had picked up the (1..3) error.
> I actually have written 2 programs for this assignment. One works well,
the
> other is a different approach to what we have been taught. Let me point
out
> that I am an external student studying this, which makes it hard as I
don't
> have any one to bounce ideas off or get any helpful input. So any help
> whether pointers or snippets of code are really appreciated.
> I do understand the need to do this by myself but it just gets
frustrating.
>

For validating data entry it is sometimes convenient to use a loop that will
not exit until a valid entry is made:

  ReadLoop:
    loop
      begin
        Put( "Enter Value > " );
        Get( value );
        exit ReadLoop when value >= 1 and value <= 10;
      exception
          when others =>
              null;
      end;
      Put_Line( "Invalid Entry - please enter a value between 1 and 10" );
    end loop;

I hope this helps,
SteveD

Re: Exit Loop_Statement

[Robert Dewar]

In article <3917C83E.D088C4DF@bton.ac.uk>,
  John English <je@bton.ac.uk> wrote:
> That should be Clients(1..4), right?

Well yes, of course, and of course we all saw that. But don't
you think it is instructive for people to find a bug like that
for themselves. I preferred the previous post which gave a
useful pointed hint (think about whether this will ever be
true), to this one that provides the correction directly.

A hard part of computer programming is figuring out why what
you have written does not work, and learning to be careful
and avoid writing such things in the first place. Practice
is really essential in this task. The purpose of assignments
is to provide this practice, and you have to be careful that
in an attempt to be helpful you do not bypass this very
important function.

> You should convert to e.g. lower case if you want case
> insensitivity:
>   if Ada.Characters.Handling.To_Lower(Clients(1..4)) = "stop"
> then ...

Again, I would point to the reference for this routine, rather
than give the exact code, which the student can then just cut
and paste without any understanding.




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Before you buy.

Re: Exit Loop_Statement

[Robert Dewar]

In article <3917D075.243A3A01@maths.unine.ch>,
  Gautier <gautier.demontmollin@maths.unine.ch> wrote:
> >           exit Any_File when Any(I+1).Clients(1..3) =
"Stop";
> Look twice at
>   Clients(1..3)
> and
>   "Stop"
> How many letters ;-) ?
> To make insensitive: ... when To_Upper(...) = "STOP"
>
> HTH
> _____________________________________________
> Gautier  --  http://members.xoom.com/gdemont/
>


Right, this Gautier post nicely illustrates what I meant in
my previous post. Helpful hints, without giving the solution
away.

No one wants students to get frustrated, and we all know the
frustration of bumping into a bug which due to temporary
blindness of temporary loss of whatever it is that makes
one able to see things, you cannot find something and need
help. We certainly want to provide help to get past such
blocks.

It's a fine line, and one that is hard to pin down some times,
but I think if everyone in CLA who wants to help students
posting here makes the effort to think about this line, then
we can provide a more useful resource for students (though
as I mentioned in another post, it seems to me that the
professor involved really *should* be the primary resource).


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Before you buy.

Re: Exit Loop_Statement

[David Freshwater]

Hi,
   Thanks for the help....I had picked up the (1..3) error.
I actually have written 2 programs for this assignment. One works well, the
other is a different approach to what we have been taught. Let me point out
that I am an external student studying this, which makes it hard as I don't
have any one to bounce ideas off or get any helpful input. So any help
whether pointers or snippets of code are really appreciated.
I do understand the need to do this by myself but it just gets frustrating.

David
Robert Dewar <robert_dewar@my-deja.com> wrote in message
news:8f91ps$vb3$1@nnrp1.deja.com...
> In article <3917C83E.D088C4DF@bton.ac.uk>,
>   John English <je@bton.ac.uk> wrote:
> > That should be Clients(1..4), right?
>
> Well yes, of course, and of course we all saw that. But don't
> you think it is instructive for people to find a bug like that
> for themselves. I preferred the previous post which gave a
> useful pointed hint (think about whether this will ever be
> true), to this one that provides the correction directly.
>
> A hard part of computer programming is figuring out why what
> you have written does not work, and learning to be careful
> and avoid writing such things in the first place. Practice
> is really essential in this task. The purpose of assignments
> is to provide this practice, and you have to be careful that
> in an attempt to be helpful you do not bypass this very
> important function.
>
> > You should convert to e.g. lower case if you want case
> > insensitivity:
> >   if Ada.Characters.Handling.To_Lower(Clients(1..4)) = "stop"
> > then ...
>
> Again, I would point to the reference for this routine, rather
> than give the exact code, which the student can then just cut
> and paste without any understanding.
>
>
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

Exit Loop_Statement

[David Freshwater]

Hi All,
         Just a quick question about Exiting a loop. I have an assignment
where I have to Exit when "Stop" is input as a clients name, which I can do.
The problem is that it has to be case insensitive. Also I am trying to get
the exception statement in the Procedure to work to work The Procedure is as
follows :
--+++++++Buy Procedures+++++++--

             --Gets user input and calls on save_data to store

procedure Buy is

begin


    I := 0; --Initialize i
    Nof := 0; --Initialize NOF

    New_Line;
    Put("Please enter the name of the file you wish to create : ");
    Get_Line(Item => Filename, Last => P_L_C_I_F);
    New_Line;


   Any_File :
      Loop

           Put("Please enter the clients name : ");
          Get_Line(Item => Any (I + 1).Clients, Last => P_L_C);
          Put("Olympic Sponsor? (Enter True or False) : ");
          Boolean_Io.Get(Sponsor);
          exit Any_File when Any(I+1).Clients(1..3) = "Stop";
          I := I + 1;  --Increment counter if name<> STOP

          Skip_Line;
          Put("Please enter the number of tickets purchased : ");
          Integer_Io.Get(Item => Any (I + 1).Num_Tickets);
          Put("Please enter the total cost of purchase : $");
          Float_Io.Get(Item => Any (I + 1).Cost_Total);
          New_Line(3);
          Skip_Line;


    end loop Any_File;

    exception

   when DATA_ERROR|NUMERIC_ERROR =>


     Put_Line("                  *****************************");
     New_Line;
     Put_Line("                  *   INCORRECT DATA ENTRY !  *");
     New_Line;
     Put_Line("                  *  Please re-enter the data *");
     New_Line;
     Put_Line("                  *****************************");
     Skip_Line;
     New_Line (2);


   Save_Data(I, Filename, P_L_C_I_F);

end Buy;

Any help or suggestions would be greatly appreciated.

David

Re: Exit Loop_Statement

[Ken Garlington]

"David Freshwater" <dafresh@cyllene.uwa.edu.au> wrote in message
news:8f7oep$khc$1@enyo.uwa.edu.au...
> Hi All,
>          Just a quick question about Exiting a loop. I have an assignment
> where I have to Exit when "Stop" is input as a clients name, which I can
do.
> The problem is that it has to be case insensitive.

One typical approach is to convert both sides of the comparison to a known
case.

> Also I am trying to get
> the exception statement in the Procedure to work to work

What have you tried?

> The Procedure is as follows :

Just out of curiosity, does this line cause the loop to exit under *any*
conditions?
>           exit Any_File when Any(I+1).Clients(1..3) = "Stop";

Also, should the loop exit when someone enters sto? How about STOPPER?

>           I := I + 1;  --Increment counter if name<> STOP
>
>           Skip_Line;
>           Put("Please enter the number of tickets purchased : ");
>           Integer_Io.Get(Item => Any (I + 1).Num_Tickets);
>           Put("Please enter the total cost of purchase : $");
>           Float_Io.Get(Item => Any (I + 1).Cost_Total);
>           New_Line(3);
>           Skip_Line;
>
>
>     end loop Any_File;
>
>     exception
>
>    when DATA_ERROR|NUMERIC_ERROR =>
>
>
>      Put_Line("                  *****************************");
>      New_Line;
>      Put_Line("                  *   INCORRECT DATA ENTRY !  *");
>      New_Line;
>      Put_Line("                  *  Please re-enter the data *");
>      New_Line;
>      Put_Line("                  *****************************");
>      Skip_Line;
>      New_Line (2);
>
>
>    Save_Data(I, Filename, P_L_C_I_F);
>
> end Buy;
>
> Any help or suggestions would be greatly appreciated.
>
> David
>
>

Re: Exit Loop_Statement

[Gautier]

>           exit Any_File when Any(I+1).Clients(1..3) = "Stop";
Look twice at
  Clients(1..3)
and
  "Stop"
How many letters ;-) ?
To make insensitive: ... when To_Upper(...) = "STOP"

HTH
_____________________________________________
Gautier  --  http://members.xoom.com/gdemont/

Re: Exit Loop_Statement

[John English]

David Freshwater wrote:
> procedure Buy is
> begin
>   [...snip...]
>    Any_File :
>       Loop
> 
>            Put("Please enter the clients name : ");
>           Get_Line(Item => Any (I + 1).Clients, Last => P_L_C);
>           Put("Olympic Sponsor? (Enter True or False) : ");
>           Boolean_Io.Get(Sponsor);
>           exit Any_File when Any(I+1).Clients(1..3) = "Stop";

That should be Clients(1..4), right?

You should convert to e.g. lower case if you want case insensitivity:
  if Ada.Characters.Handling.To_Lower(Clients(1..4)) = "stop" then ...

>     [...snip...]
>     end loop Any_File;
> 
>     exception
> 
>    when DATA_ERROR|NUMERIC_ERROR =>

You should really use Constraint_Error instead of Numeric_Error (although
they both mean the same thing).

Also, don't you want the exception to be handled inside the loop so the
user can re-enter the data? At the moment, it'll print an error message,
call Save_File, and then you're at the end of the program...

Try something like this:

   loop
     begin
       ...
     exception
       ...
     end;
   end loop;

Your exit statement will get you out of the loop; an exception will be
handled by the exception handler inside the loop, so after you've handled
the exception you'll go round the loop again.
HTH,

-----------------------------------------------------------------
 John English              | mailto:je@brighton.ac.uk
 Senior Lecturer           | http://www.it.bton.ac.uk/staff/je
 Dept. of Computing        | ** NON-PROFIT CD FOR CS STUDENTS **
 University of Brighton    |    -- see http://burks.bton.ac.uk
-----------------------------------------------------------------

Re: Exit Loop_Statement

[John English]

Robert Dewar wrote:
> In article <3917C83E.D088C4DF@bton.ac.uk>,
>   John English <je@bton.ac.uk> wrote:
> > That should be Clients(1..4), right?
> 
> Well yes, of course, and of course we all saw that. But don't
> you think it is instructive for people to find a bug like that
> for themselves. I preferred the previous post which gave a
> useful pointed hint (think about whether this will ever be
> true), to this one that provides the correction directly.

I would agree with you completely if the question had been "Why
does this code generate a Constraint_Error?" But it wasn't, so
I pointed out an unrelated minor typo in passing. Maybe he hit
the key next to the 4 by mistake. Maybe it was a deliberate error
to generate Constraint_Error for testing purposes.

> A hard part of computer programming is figuring out why what
> you have written does not work, and learning to be careful
> and avoid writing such things in the first place. Practice
> is really essential in this task. The purpose of assignments
> is to provide this practice, and you have to be careful that
> in an attempt to be helpful you do not bypass this very
> important function.

I know you don't like people giving direct answers to questions,
but I hadn't realised this also extended to questions that haven't
even been asked...

-----------------------------------------------------------------
 John English              | mailto:je@brighton.ac.uk
 Senior Lecturer           | http://www.it.bton.ac.uk/staff/je
 Dept. of Computing        | ** NON-PROFIT CD FOR CS STUDENTS **
 University of Brighton    |    -- see http://burks.bton.ac.uk
-----------------------------------------------------------------

Re: Exit Loop_Statement

[John English]

John English wrote:
> I would agree with you completely if the question had been "Why
> does this code generate a Constraint_Error?"

Just before Robert roasts me again, let me point out that my talking
about Constraint_Error was due misremembering the original code as
involving an assignment Clients(1..3) := "Stop". I've just revisited
the code and now I'm going to go and wipe the egg off my face.

-----------------------------------------------------------------
 John English              | mailto:je@brighton.ac.uk
 Senior Lecturer           | http://www.it.bton.ac.uk/staff/je
 Dept. of Computing        | ** NON-PROFIT CD FOR CS STUDENTS **
 University of Brighton    |    -- see http://burks.bton.ac.uk
-----------------------------------------------------------------

Re: Exit Loop_Statement

[Robert A Duff]

"Jeff Creem" <jcreem@atetola.mv.com> writes:

> Take a look at the following snippet of code..
> 
> >     I := 0; --Initialize i
> >     Nof := 0; --Initialize NOF
> 
> After reading the comments, is there anything that you now know that you did
> not know before you read the
> comments....Nope....

Well, I wouldn't expect to see comments like that in
professionally-written code, but I don't think it's so bad for a
beginner to write comments like that.  Somebody who doesn't know how to
program, and/or doesn't know the programming language they're using very
well, can benefit from comments that remind them of the language
semantics.  Once they learn the language well, they can easily
learn to write better comments.  It's easier than *not* commenting early
on, and then later learning to do so.

By the way, here's an example of the kind of comments you're complaining
about.  This comes from an ACATS test, which is testing the pragma
Import feature for interfacing Ada code and C code.  It's so bad that
I think the author of this code must have been doing it as a joke.
I mean, it's got one simple line of executable code, and several
paragraphs explaining in detail how it works!

/*
-- CD30051.C                                                            
--                                                                       
--                             Grant of Unlimited Rights
--
--     Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687 and
--     F08630-91-C-0015, the U.S. Government obtained unlimited rights in the
--     software and documentation contained herein.  Unlimited rights are 
--     defined in DFAR 252.227-7013(a)(19).  By making this public release, 
--     the Government intends to confer upon all recipients unlimited rights
--     equal to those held by the Government.  These rights include rights to
--     use, duplicate, release or disclose the released technical data and
--     computer software in whole or in part, in any manner and for any purpose
--     whatsoever, and to have or permit others to do so.
--
--                                    DISCLAIMER
--
--     ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR
--     DISCLOSED ARE AS IS.  THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED 
--     WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE
--     SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE 
--     OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A
--     PARTICULAR PURPOSE OF SAID MATERIAL.
--*
--                                                                       
-- FUNCTION NAME: _cd3005_1
--                                                                       
-- FUNCTION DESCRIPTION:                                                 
--      This C function returns the sum of its parameter and 1 through
--      the function name.  The parameter is unchanged.
--
-- INPUTS:
--      This function requires that one parameter, of type int, be passed 
--      to it.
--
-- PROCESSING:
--      The function will calculate the sum of its parameter and 1
--      and return this value as the function result through the function
--      name.
--
-- OUTPUTS:                        
--      The sum of the parameter and 1 is returned through function name. 
--                                                                       
-- CHANGE HISTORY:                                                       
--      12 Oct 95   SAIC    Initial prerelease version.                  
--      14 Feb 97   PWB.CTA Created this file from code appearing in
--                          CD30005.A (as comments).
--!
*/
            int _cd30005_1( Value )
            {
                /* int Value */

               return Value + 1;
            }

Re: Exit Loop_Statement

[Jeff Creem]

By the way...Not that this was the original question and it is probably help
"out of scope"
but so manner programmers (even those who have been doing it for a living
for a few years) do this that
I thought it worth while to catch this now..

Take a look at the following snippet of code..

>     I := 0; --Initialize i
>     Nof := 0; --Initialize NOF
>


After reading the comments, is there anything that you now know that you did
not know before you read the
comments....Nope....Just a case of commenting so that one can feel good that
there are comments in the
code...Use better variable names and delete those comments...(Of course
there are other
more subtle things that could be done on those lines as well but that is
left as an exercise for the writer)

Jeff