in reply to The error says the value is uninitialized, but it works anyway

Looks like you have been well taken care of regarding your inquiry, but I would like to add a cool use of each I recently discovered. Should fit well with your code assignment. You can use each to collect the indices of an array, or both indices and values. From the docs: 
 each HASH
 each ARRAY
            When called on a hash in list context, returns a 2-element list
            consisting of the key and value for the next element of a hash. In
            Perl 5.12 and later only, it will also return the index and value
            for the next element of an array so that you can iterate over it;
            older Perls consider this a syntax error. When called in scalar
            context, returns only the key (not the value) in a hash, or the
            index in an array.
So, using each, your code can go from: 
$ perl -e '
my @colors = qw(red green blue yellow pink purple brown);
my $count = @colors;
my @drop = qw(pink brown);
my $num = 0;
foreach $num (1..$count){  
    $num--;
    if ($colors[$num] eq $drop[0] or $colors[$num] eq $drop[1]){ 
        splice (@colors, $num, 1);  
    }
}
print "@colors \n";
'

[download]
to: 
$ perl -e '
my @colors = qw(red green blue yellow pink purple brown);
my @drop = qw(pink brown);
while ( my ($num, $val) = each @colors ) {
  if ($val eq $drop[0] or $val eq $drop[1]) {
    splice (@colors, $num, 1);
  }
}
print "@colors \n";
'

[download]
both produce the following output: 
__output__
red green blue yellow purple

[download]

I hope that was the correct answer! :)

Replies are listed 'Best First'.
Re^2: The error says the value is uninitialized, but it works anyway
by AnomalousMonk (Archbishop) on Aug 18, 2019 at 06:34 UTC

    Unfortunately, it's still altering an array (or it might have been a hash) over which you're iterating and so still incorrect: 

    c:\@Work\Perl\monks>perl -wMstrict -le
"my @colors = qw(red green blue yellow pink purple brown);
 my @drop = qw(pink purple);
 while ( my ($num, $val) = each @colors ) {
   if ($val eq $drop[0] or $val eq $drop[1]) {
     splice (@colors, $num, 1);
   }
 }
 print qq{@colors};
"
red green blue yellow purple brown

    [download]

    Update: each sez:

    If you add or delete a hash's elements while iterating over it, the effect on the iterator is unspecified; for example, entries may be skipped or duplicated--so don't do that.
    The same obviously applies to arrays. The each doc goes on to discuss a specific exception involving delete and hashes, but still no joy WRT arrays.

    Give a man a fish:  <%-{-{-{-<

[reply]
[d/l]
[select]
      Ahh, of course... thanks!

      adding "save" array, and "if" to "unless"...

      perl -wMstrict -e '
my @colors = qw(red green blue yellow pink purple brown);
my @drop = qw(pink purple);
my @save = ();
while ( my ($num, $val) = each @colors ) {
  unless ($val eq $drop[0] or $val eq $drop[1]) {
    push @save, $colors[$num];
  }
}
print "@save \n";
'
__output__
red green blue yellow brown

      [download]
[reply]
[d/l]

In Section Seekers of Perl Wisdom