Re: do until loop breaks before meeting the condition

Hi, I have just tried the following code:

use strict;
use warnings;
use constant MAXBYTES => scalar 5;

my $result;

$| = 1;
MSG: 
    print "Please be aware maximum length 255 characters!:\n"; 
    
do {
    print "Send this text to clients:\n\n";
    chomp ($result = <STDIN>);
    if (length($result) >= MAXBYTES) {
    print "\nYou have reached the limit of characters ".length($result
+)."!\n\n";
    goto MSG;
    }
} until ($result eq "END" or $result eq "end");
$| = 1;
[download]

and it works as expected for me: it loops when I enter strings such as "foo" or "bar" and exits the loop if I enter "end" or "END".

Having said that, there are a few problems in this code. One is that the message states:

print "Please be aware maximum length 255 characters!:\n";
[download]

but MAXBYTES is set to 5. The second one is the use of goto, this is widely considered to be a very bad programming practice, especially when the goto brings you upward in your code and out of a loop, and this is pretty useless in this case. Try something like this instead:

use strict;
use warnings;
use constant MAXBYTES => scalar 5;

my $result;

$| = 1;
my $msg = "Please be aware maximum length 255 characters!:\n"; 
    
do {
    print "Send this text to clients:\n\n";
    chomp ($result = <STDIN>);
    if (length($result) >= MAXBYTES) {
         print "\nYour input has a length of " . length($result) . "; 
+the limit is ". MAXBYTES, "\n\n";
         print $msg;
    }
} until (uc ($result) eq "END");
$| = 1;
[download]

although this is still somewhat clunky (but I wanted to stay close to your code). One additional question: why are you setting $| twice to the same value?

On the problems with the goto function, please read this classical text: http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html.

Comment on Re: do until loop breaks before meeting the condition Select or Download Code

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Re^2: do until loop breaks before meeting the condition by LanX (Saint) on Jun 08, 2014 at 16:28 UTC
ehm ... he's using `goto` as loop control, `last`, `next` and `redo` are not much different. Than you don't print the `$msg` before first run like he did. Considering "cleanest" and "DRYest" flow control , I'd rather try this `> perl $max_length=5; OUTER: { print "Input max is $max_length!!!\n"; while (1) { chomp( $input = <STDIN> ); last OUTER if lc( $input ) eq "end"; redo OUTER if length( $input ) > $max_length; print "- $input is OK\n"; } } __END__ Input max is 5!!! 1 - 1 is OK 12345 - 12345 is OK 123456 Input max is 5!!! 123 - 123 is OK end >` [download] YMMV! :) update please note that the more verbose `OUTER: while(1) { ...` [download] works equally well and might be less surprising for some maintainers. :) Cheers Rolf (addicted to the Perl Programming Language)	[reply] [d/l] [select]
Re^3: do until loop breaks before meeting the condition by thanos1983 (Parson) on Jun 08, 2014 at 18:50 UTC
To: Lanx, Thanks, I was not even aware of: `last, next and redo`. Hmmm based on second look your solution looks simple and I ques better than mine. I think I will follow it. Again thank you for your time and all this information that you shared. Seeking for Perl wisdom...on the process...not there...yet!	[reply] [d/l]
Re^3: do until loop breaks before meeting the condition by Laurent_R (Canon) on Jun 09, 2014 at 06:22 UTC
Well, I am not an anti-goto fanatic, the comment on gotos was just one out of 3 comments. I still think it is much better to use regular loop control statements (last, next, etc.), and it is most of the time best to avoid `goto`s altogether (except for the special `goto &name` construct).	[reply] [d/l] [select]
Re^2: do until loop breaks before meeting the condition by thanos1983 (Parson) on Jun 08, 2014 at 18:33 UTC
To: Laurent_R, Thanks for the information I was not aware that `goto` is bad coding. I removed it and followed your example. P.S.: The MAXBYTES = 5 is just for fast implementation purposes. P.S.2 About the `$\| = 1;` I thought that it would be good to flush the buffer also at the output. Maybe I was just over doing it. Again thank you for your time and effort. Seeking for Perl wisdom...on the process...not there...yet!	[reply] [d/l] [select]

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