I am a beginner Perl student. I want to find different ways to do loops and modify an array from a function. So, here is what I have written so far. The last one ChangeArray6() doesn't work, and I don't know why. Also, what's the best way to deal with arrays? If my sub needs to change an array's contents, how should I write my code? What's the neatest, best, most memory-efficient way to do it from a sub?

use strict;
use warnings;

my @A = (0) x 20;

PrintA(); ChangeArray1();
PrintA(); ChangeArray2(@A);
PrintA(); ChangeArray3(@A);
PrintA(); ChangeArray4(@A);
PrintA(); ChangeArray5(\@A);
PrintA(); ChangeArray6(@A);
PrintA();

#
# This function changes an array
#
sub ChangeArray1
{
  my $i = 0;
  LOOP:
    return if ($i >= @A);
    $A[$i++] = 1;      # Write to global array
  goto LOOP;
}

sub ChangeArray2
{
  my $REF = \@_;       # get reference

  for (my $i = 0; $i < @$REF; $i++)
  {
    $$REF[$i] = 2;
  }
}

sub ChangeArray3
{
  foreach my $X (@_)   # $X = reference to each item
  {
    $X = 3;
  }
}

sub ChangeArray4
{
  my $i = @_;
  while ($i-- > 0)
  {
    $_[$i] = 4;        # use direct reference
  }
}

sub ChangeArray5
{
  my $B = shift;       # I don't understand this, but it works :P

  foreach my $X (@$B)
  {
    $X = 5;
  }
}

sub ChangeArray6
{
  @_ = (6) x @_;       # This does not work.
}

sub PrintA { print "\n".join('', @A); }
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