$ perl5100 -we 'my ($x,@y); $x=$y[0]+1'
Use of uninitialized value $y[0] in addition (+) at -e line 1.

$ perl5100 -we 'my ($x,@y); $x=$y[0]+$y[1]'
Use of uninitialized value in addition (+) at -e line 1.
Use of uninitialized value in addition (+) at -e line 1.
$