$data[ $#data ++ ] = $1;

##</code><code>##

use warnings;
my @data;
for( 1..3 ) {
    $data[ $#data ++ ] = $_;
}
for (@data) {
    print $_,"\n";
}
__END__
2
3
Use of uninitialized value $_ in print at - line 7.


##</code><code>##

use warnings;
my @data;
for( 1..3 ) {
    $data[ ++ $#data ] = $_;
}
for (@data) {
    print $_,"\n";
}
__END__
1
2
3