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use strict;
my @array1=qw(1 2 3 4);
...
           print $array1[$i] - $array2[$i],"\n";
           $i++;
           }

#Descending 
my $i = $#array1+1; 
...
# my $i = @array1;

print $array1[$i] -$array2[$i],"\n" while $i--;