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From: "SteveD" <nospam_steved94@attbi.com>
Newsgroups: comp.lang.ada
References: <93d4dcd4.0210031020.b0cca2b@posting.google.com>
Subject: Re: Newbie question on Ada TExt_IO
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"Justin" <jbirtwell@yahoo.com> wrote in message
news:93d4dcd4.0210031020.b0cca2b@posting.google.com...
> Hi,
[snip]
>
> X:Integer;
> ...
> Put("Please enter a number between 1 and 6);
> Get(x);
>
> But what if they give me 'abc' or 4.44 or simply
> 1230000000000000000000000000000000000000000000000000000000000000000000000
>
> How can I handle this?  From my take on what I've read I should avoid
> exception handling for things I'm not expecting, so I've ruled out
> exceptions, that leaves me with obtaining a value of generic type and
> evalutating the type at run-time...how can I do this?  Is this the
> right strategy?

I suggest that you handle this differently depending on the target audience
(or "user" if you prefer).

If I am putting together a small program for internal use, I typically use a
small loop with an exception handler... something along the lines of (pseudo
code):

  loop
    begin
    Prompt for input
    Get input
    Exit when input is valid
    exception
      when others =>
         Display a nastygram about invalid input
    end;
  end loop;
  skip to the next line of input

If I am putting something together for external use, I would read the value
into a string using something like Text_Io.Read_Line with the string
ridicuously large (maybe 1..256).  If after reading the string the value of
"last" is the size of the string, I know something is wrong and report an
error (unlikely to happen, but handled).  Once I get a reasonably sized
string, I trim leading and trailing spaces using Ada.Fixed.Trim.  Then I
check for valid characters using something like Ada.Strings.Fixed.Index to
make sure the numeric input contains only digits.  Then I use the
Integer'Value to get the actual value of the numeric string.  Just to be
safe the Integer'Value conversion is protected by an exception handler.

These days most programs for external use are GUI's, which change the rules
a bit but still require validation.

I hope this helps,
SteveD