It's actually all three generating the warning.

What you need is:

for my $i (0 .. $#titles){
    ...
}
[download]

Note the $#titles as opposed to @titles. You're essentially causing an off-by-one issue by using the array count as opposed to the element position (index). Example:

perl -wMstrict -E 'my @x=(qw(a b c)); say "$_: $x[$_]" for (0..@x)'
0: a
1: b
2: c
Use of uninitialized value in concatenation (.) or string at -e line 1
+.
3:
[download]

vs:

perl -wMstrict -E 'my @x=(qw(a b c)); say "$_: $x[$_]" for (0..$#x)'
0: a
1: b
2: c
[download]