What could be the exact usage of While

jesuashok has asked for the wisdom of the Perl Monks concerning the following question:

esteemed monks,

#!/usr/bin/perl
use strict;

my $i = 0 ;

while ( $i < 10 ) {
     print "Hello World\n";
     
} continue {
     $i ++;
}
[download]

#!/usr/bin/perl
use strict;

my $i = 0 ;

while ( $i < 10 ) {
     print "Hello World\n";
     $i ++;
}
[download]

whatever code written using while ( <condition> ) { } continue { } can be written using simple while ( <condition> ) { }. So, I would like to know the exact usage of while () {} continue {} loop.

I am very sorry to bother you if this has been discussed already in perlmonks.

Comment on What could be the exact usage of While - continue loop Select or Download Code

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Re: What could be the exact usage of While - continue loop by GrandFather (Saint) on May 09, 2007 at 03:36 UTC
A common usage of continue is to allow some loop-end code to execute even when next is used to provide an early exit from a loop iteration. Consider: `use warnings; use strict; for my $yodda (1 .. 4) { print "Odd is " and next if $yodda & 1; print "Even is "; } continue { print "$yodda\n"; }` [download] Prints: `Odd is 1 Even is 2 Odd is 3 Even is 4` [download] Often early exits are used to avoid excessive control structure nesting - especially of `if` controlled blocks DWIM is Perl's answer to Gödel	[reply] [d/l] [select]
Re: What could be the exact usage of While - continue loop by naikonta (Curate) on May 09, 2007 at 04:18 UTC
The continue block is guaranteed to be executed in each iteration. `my $i = my $j = 0; while ($i++ < 5) { next if $i == 2 \|\| $i == 4; print "i:$i\n"; } continue { $j++; printf "j:$j\n"; }` [download] See that the i line is not always printed because it depends on `if` checking, while j line is always printed regardless what happens inside the `while` block^. This won't happen if printing j line is put inside the block as i. But frankly, I never use continue myself in practical. It exists for some reason regarding the `for` loop (see Programming Perl). From the doc: "last", "next", or "redo" may appear within a "continue" block. "last" and "redo" will behave as if they had been executed within the main block. So will "next", but since it will execute a "continue" block, it may be more entertaining. Some monk commented on that emphasized text but I can't recall the node. Unless redo take place, as shown by GrandFather below. The same thing with last. Consider, `my $yodda = 0; while ($yodda < 6) { last if $yodda == 5; redo if ++$yodda & 1; print "Even is "; } continue { print "$yodda\n"; }` [download] Update: added note following correction by GrandFather Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!	[reply] [d/l] [select]
Re^2: What could be the exact usage of While - continue loop by GrandFather (Saint) on May 09, 2007 at 04:37 UTC
Actually the continue block is not executed for a redo. Consider: `use warnings; use strict; my $yodda = 0; while ($yodda < 4) { redo if ++$yodda & 1; print "Even is "; } continue { print "$yodda\n"; }` [download] Prints: `Even is 2 Even is 4` [download] DWIM is Perl's answer to Gödel	[reply] [d/l] [select]
Re^3: What could be the exact usage of While - continue loop by naikonta (Curate) on May 09, 2007 at 04:58 UTC
Well, you hit me at the "regardless" part then :-) Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!	[reply]
Re: What could be the exact usage of While - continue loop by davido (Cardinal) on May 09, 2007 at 06:24 UTC
continue simply allows you to add code to a loop that is guaranteed to execute on each iteration even if next is invoked. It's further documented in perlsyn. Dave	[reply]


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What could be the exact usage of While - continue loop