# 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.