sub inc_original {
   $_[0]++;
   return $_[0];
}

sub inc_refactored {
   my ($var) = @_;
   $var++;
   return $var;
}

{  my $i = 3;
   my $j = inc_original($i);
   print("$i + 1 = $j\n");    # 4 + 1 = 4
}
{  my $i = 3;
   my $j = inc_refactored($i);
   print("$i + 1 = $j\n");    # 3 + 1 = 4
}