use Data::Dumper;
my @m;
my $c;

$c = 3;
push(@{$m[$c]}, [ 'foo' ]);

$c = 2;
push(@{$m[$c]}, [ 'bar' ]);

print Dumper(\@m), "\n";
for (0..3) {
  print "length of m[$_] = ", scalar(@{$m[$_]}), "\n";
}