You have a *lot* of syntax issues that you'd see if you put

use warnings;
use strict;
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at the top of your script. Also, when I do correct the errors, I'm not sure what to expect as output. Where are @prdct and @prdct1 defined?

Please put your code in <code></code> tags as Laurent_R stated, use proper indentation, show us what the two arrays I mentioned above should have in them, and what exactly you expect as output.

-stevieb

We really need some information about the contents of the @prdct and @prdct1 arrays to figure out what you are trying to do and why, as you state, you're not entering the inner while loop.

I agree with stevieb that you should have:

use strict;
use warnings;
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Although this is not your main problem, please note that:

for ( $i = 0 ; $i <= $#res ; $i++ ) {
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for my $i (0..$#res) {
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for my $thing (@res) {
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Also, you don't need:

        else {
        }
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But these are minor things, please let us know what data you have as input and want you want to do with it. We need that to better help you.

use strict;
use warnings;
use Algorithm::Permute;

my @prdct = 55..66;
my @prdct1 = 'a'..'f';

my $product  = Algorithm::Permute->new( \@prdct );
my $product1 = Algorithm::Permute->new( \@prdct1 );


while ( my @res = $product->next ) {
  chomp @res;
  my $chk = join " + ", @res;
  print "chk:$chk\n";
  $product1->reset; # Allow to iterate again
  while (my @res1 = $product1->next ) {
      chomp @res1;
      my $chk1 = join( ' + ', @res1); 

      print "\tchk1:$chk1\n";
      my  $chk3 = "$chk <=> $chk1";
      my  $chk4 = "$chk1 <=> $chk";
  }
}
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Hey this " $product1->reset; # Allow to iterate again" suggested by NetWallah worked perfectly for my problem. Thanks a ton :) :)

BTW how to close this or vote for this answer or mark as solved???

I'm not sure you have enough XP to vote. You should be able to edit the title of the original question, though, adding a [SOLVED] notice - at least, that's what some people here do.
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

Hi Sivaratna,

1) ALWAYS "use strict;" and "use warnings;" These pragmas will reveal a lot of errors, and unexpected situations, like for example a variable being empty when you expected it to have a value, because you'll get a warning about it being "uninitialized" -- this will tip you off to where the problem is.

2) Learn to use the Data::Dumper module as you develop your code. Then you can liberally use debugging statements that will show what is in the variables at each step of your program, rather than just waiting until the end to see whether or not it failed. Like this:

#!perl
use strict;
use warnings;
use feature qw/ say /;
use Data::Dumper;
use Algorithm::Permute;

## Some code here that produces @prdct ...

my $product = Algorithm::Permute->new( \@prdct );

say Dumper( $product ); # did you get what you expected?

while ( my @res = $product->next ) {
  say Dumper( @res ); # now did you get what you expected?
  # do something else ...
}
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Remember, laziness is a virtue for a programmer, but laziness may not be what you think it is! Put in the work to make your code pass through strict, warnings, Perl::Critic, and so on, and put in the work to add debugging info and testing, and your life will be easier as you go forward!!

Please put your code between <code> and </code> tags in order to preserve the formatting (especially code indentation which I hope that you are using). Right now, your code is very difficult to read, especially when it comes to nested loops.