scoping inside the loop

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

Case1:

do 
{
   $i=0;
   print"the value of i inside the loop is :$i\n";
   $i++;
}until($i<=10)
[download]

On executing above script i am getting output the value of i inside the loop is :0 .I am expecting the loop should execute.Please clarify

Case2:

use strict;
my $i=5;
do
{
   print"the value of i is :$i\n";
   $i--;
}until($i<=0);
[download]

This program is executing as expected

Case3:

use strict;
my $i=5;
print "the value of i outside the loop is $i\n";
do
{
   print"now i entered inside the loop \n";
   my $i=10;
   print "the value of i inside the loop is :$i\n";
   $i--;
}until($i<=0);
[download]

This is failing to go through the loop. Please clarify why scoping inside the loop is not getting triggered.

Comment on scoping inside the loop Select or Download Code

Replies are listed 'Best First'.
Re: scoping inside the loop by LanX (Saint) on May 17, 2013 at 17:59 UTC
Case1: you're resetting $i each time at the beginning Case3 the $i scoped within the block is differentą from the outer one (update: and you are resetting the inner one each time again) Generally better use prefix-constructs like `while () {...}`, `until () {...}` or `for (;;) {...}` e.g. Case 3: `use strict; use warnings; my $i=42; print "outside: $i\n"; for (my $i=5; $i>0; $i--) { print "inside: $i\n"; }; print "outside: $i\n"; my $j=666; print "outside: $j\n"; { my $j=5; do { print"inside: $j\n"; $j--; } until($j<=0) } print "outside: $j\n";` [download] prints: `outside: 42 inside: 5 inside: 4 inside: 3 inside: 2 inside: 1 outside: 42 outside: 666 inside: 5 inside: 4 inside: 3 inside: 2 inside: 1 outside: 666` [download] As you can see, does the postfix construction force you to an extra block to limit the scope of the inner $j. Cheers Rolf ( addicted to the Perl Programming Language) Update expanded code example Footnotes 1) see Coping with Scoping	[reply] [d/l] [select]
Re^2: scoping inside the loop by Anonymous Monk on May 17, 2013 at 18:36 UTC
Thanks LanX.Understood but in second case which is a working condition $i's scope is in outer loop but how it got tucked in to inside loop.My understanding is if my is before a variable it's existence is strictly with in that boundary. In case 2 my is associated with $i so i think it only resides outside or where it is defined but i am confused how it got transported to loop.	[reply]
Re^3: scoping inside the loop by LanX (Saint) on May 17, 2013 at 18:40 UTC
No, up to the point that you declare an inner $i with `my` the outer one is used. No inner `my $i` means the outer one is everywhere available. These are universal rules for lexical variables in almost any language! Have a look at the scoping-article I linked. Cheers Rolf ( addicted to the Perl Programming Language)	[reply] [d/l] [select]
Re: scoping inside the loop by hdb (Monsignor) on May 17, 2013 at 19:00 UTC
case 1 does not loop because the "until" condition is met immediately ($i=1 which is less then 10).	[reply]
Re^2: scoping inside the loop by LanX (Saint) on May 17, 2013 at 19:06 UTC
and otherwise it's an endless-loop Cheers Rolf ( addicted to the Perl Programming Language)	[reply]
Re^3: scoping inside the loop by Anonymous Monk on May 17, 2013 at 21:55 UTC
That makes clear	[reply]

Update

Footnotes