The following is a real bug that appeared in real code by yours truly. (Code which was written late at night under pressure. *ahem*)

I think that trying to see what causes a possible infinite loop in this code is rather instructive. 

sub init_selections {
  my $self = shift;
  my $slice_count = shift;

  my $cur_balances = $self->{cur_balances};
  my $balance = 0;
  $balance += $_ foreach @$cur_balances;

  my @selections;
  my $select = 0;
  my $cur_balance = $cur_balances->[0];
  foreach my $i (1..$slice_count) {
    # Move move selected forward until we are at the current
    # position.
    while ($cur_balance < ($balance * $i / $slice_count)) {
      $cur_balance += $cur_balances->[++$select];
    }
    push @selections, $select;
  }
  return $self->{selections} = \@selections;
}

[download]
(Assume that the cur_balances are all positive numbers greater than 10,000, and their sum is under 2 billion.)

UPDATE
Oops, forgot to ask. Please hide answers as described in How to present spoilers :-). Thanks.

UPDATE 2
mdillon pointed out to me that I should mention that "billion" here is the US billion, ie 10**9. Also the slice count may be assumed to be an integer in the range 5-100.

In reply to Instructive bug by tilly

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