in reply to Boolean counter?

Two more approaches:

- Using hashes:

  my %Next = ( 0 => 1, 1 => 0);
  my $Counter = 0;
  #...
  $Counter = $Next{$Counter};

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- Decreasing instead of increasing:

  $Counter = abs --$Counter;

[download]

Replies are listed 'Best First'.
Re^2: Boolean counter?
by shawnhcorey (Friar) on Dec 07, 2009 at 14:07 UTC
    $Counter = - --$Counter;
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[d/l]

      Don't modify a variable that you're using elsewhere in an expression. At best, it's unclear. At worse, the result is undefined. 

      $toggle = - --$toggle;

      [download]
      should be 
      $toggle = -( $toggle - 1 );

      [download]
      which can be shortened to previously mentioned 
      $toggle = 1 - $toggle;

      [download]
[reply]
[d/l]
[select]
      The behaviour of that is actually not defined. You may end up with $Counter being -1, or with purple daemons coming out of your USB port, ready to chew off your fingers.
[reply]
        $i appears only once, the behaviour is defined 
        $ perl -MO=Deparse,-p -le"print - --$i"
BEGIN { $/ = "\n"; $\ = "\n"; }
print((-(--$i)));
-e syntax OK

        [download]
        You were thinking of 
        print(-( ++$i - --$i ))

        [download]
[reply]
[d/l]
[select]
        What about it is not defined?
[reply]

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