An ascending or descending index accessing of each of the arrays using a while loop..

use strict;
my @array1=qw(1 2 3 4);
my @array2=qw(4 3 2 1);

#ascending 
my $i =0;
while($i<= $#array1){
           print $array1[$i] - $array2[$i],"\n";
           $i++;
           }
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#Descending 
my $i = $#array1+1; 
#or
# my $i = @array1;

print $array1[$i] -$array2[$i],"\n" while $i--;
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UPDATED: Comments added...