$m = 20;  print ++$m + $m++;

##</code><code>##

  $m = 20;  print noop(++$m) + $m++;

  sub noop{ return shift }

##</code><code>##

   # This is an attempt at emulating ++$m with preInc($m)
   sub preInc {
     $_[0] = $_[0] + 1;     # Increment input argument (the side effect),
     return $_[0];          # and return the new, incremented value.
   }

   # And this is an attempt at emulating $m++ with postInc($m)
   sub postInc {
     my $temp = shift;      # Remember original value,
     $_[0] = $_[0] + 1;     # increment input argument (the side effect),
     return $temp;          # and return the old, un-incremented value.
   }

   my $m = 20;
   print preInc($m) + $postInc($m);   # This prints 42.
                                      # The final value is $m is 22.

##</code><code>##

   my $m=20; 
   print ++$m + $m++;           # This prints 43 !
                                # The final value is $m is still 22.

##</code><code>##

   # Print values and addresses of passed argument and $m.
   sub look {
     print "look was passed '" . $_[0] . "' at . \$_[0] . ".\n";
     print "while \$m is '" . $m . "' at " . \$m . ".\n";
     return $_[0];
   }

   my $m = 20;
   my $p = look(++$m) + look($m++);
   print $p;

##</code><code>##

   sub noop {        # do nothing
    return shift;
   }
  
   my $m=20; print noop(++$m) + $m++;     # This prints 42 !

##</code><code>##

   ==== increment weirdness: ++$m + $m++ ==========
   m = 20 at 0x80ab23c 
   p = ++m + m++ 
     *** inc  0x80ab23c : 20 --> 21 
          m is 21 at 0x80ab23c 
     *** copy 0x80ab23c --> 0x804c120 
          m is 21 at 0x80ab23c 
     *** inc  0x804c120 : 21 --> 22 
          m is 22 at 0x804c120 
     *** add : 22 at 0x804c120 + 21 at 0x80ab23c = 43 at 0x80ab11c 
          m is 22 at 0x804c120 
   p = 43 at 0x80ab11c