bitwise_demo.php

<pre><?php
// Gisthub Git to support StackOverflow question http://stackoverflow.com/questions/3391193/notification-preferences-predicament/3391599#3391599

    switch($_GET['x']) { // Was POST, but when playing around with the code GET makes more sense.
       case 'Email': $x = pow(2,0); echo "X Email"; break; // 1
       case 'Sms':   $x = pow(2,1); echo "X Sms"; break; // 2
       case 'Both':  $x = pow(2,0) + pow(2,1); echo "X Both"; break;// 3, since 1 + 2 = 3.
       default: $x = 0;
    }

    switch($_GET['y']) { // Was POST, but when playing around with the code GET makes more sense.
       case 'Email': $y = pow(2,2); echo "Y Email"; break; // 4
       case 'Sms':   $y = pow(2,3); echo "Y SMS"; break; // 8
       case 'Both':  $y = pow(2,2) + pow(2,3); echo "Y Both"; break; // 12, since 4 + 8 = 12.
       default: $y = 0;
    }
    
    $z = $x + $y;
    
    var_dump($x);
    var_dump($y);
    var_dump($z);
    
    // Now, we can detect Email or SMS using the bitwise values.
    if($z & 1) echo "X Email";
    if($z & 2) echo "X SMS";
    if($z & 4) echo "Y Email";
    if($z & 8) echo "Y SMS";