Re: [ot... well kindof] SDI

["chris.danx" <spamoff.danx@ntlworld.com>]

Chad R. Meiners wrote:
> "chris.danx" <spamoff.danx@ntlworld.com> wrote in message

>>   - "the following procedures use result codes:
>>      ...
>>
>>      Modify the procedures to use exceptions instead, ensuring that the
>>      effect is the same."
> 
> 
> I think this question would be suitable here since you can show both
> versions of the code and ask specific questions about the codes'
> equivalance.

this is the original code.


subtype Postcode is String (1..7);

type PersonRecord is
    record
       name    : ...;
       address : ...
       pc      : Postcode;
    end record;

-- Read a postcode from standard input into code.
-- Set ok to true if and only if that post code is
-- well-formed.
--
procedure get_postcode (pc : out Postcode;
                         ok : out Boolean) is
begin
    get (pc);
    ok := is_letter(pc(1)) and ...;
end get_postcode;


-- Read complete personal details from standard input into person,
-- interactively promting the user for each detail.
--
procedure get_personal_details (person : out PersonRecord) is
    pc_ok : Boolean;
begin
    ... -- read person.name and person.address.
    loop
       put ("enter postcode");
       get_postcode (person.pc, pc_ok);
       exit when pc_ok;
       put_line ("postcode is ill-formed!");
     end loop;
end get_personal_details


This is my revision to make it work with exceptions instead.

subtype Postcode is String (1..7);

type PersonRecord is
    record
       name    : ...;
       address : ...
       pc      : Postcode;
    end record;

postcode_error : exception;

-- return true if pc is well-formed, false otherwise.
--
-- I prefer this since postcode formats may change in future,
-- this makes a change easier!
--
function is_wellformed (pc : in postcode) return boolean  is ...;


-- Read a postcode from standard input into code.
--
-- raises a Postcode_Error exception if the postcode is ill-formed.
--
procedure get_postcode (pc : out Postcode) is
begin
    get(pc);
    if not is_wellformed (pc) then
       raise Postcode_Error;
    end if;
end get_postcode;

-- Read complete personal details from standard input into person,
-- interactively promting the user for each detail.
--
procedure get_personal_detials (person : out PersonRecord) is
begin
    ... -- read person.name and person.address.
    loop
       begin
          put ("enter postcode");
	
          get_postcode (person.pc, pc_ok);
          exit;  -- ???
       exception
          when Postcode_Error => Put_Line ("Postcode is ill-formed!");
       end;
     end loop;
end get_personal_details


My concern is at the line marked "-- ???" the code will just exit the 
begin-end block not the loop, is this correct?  If so a simple revision 
that introduced a flag set after get_postcode would do.

The effect of the code has to be the same, that is it must loop until a 
valid postcode is entered.



Chris

-- 
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