$ perl -e'   @a = qw( abc def );
             $a[-1] = "ghi";
             $a[-2] = "jkl";
             $a[-3] = "mno";       '
Modification of non-creatable array value attempted, subscript -3 at -e line 4.

##</code><code>##

while ( --$i )

##</code><code>##

while ( --$i > 0 )