<?php
  $a = $b = $c= 0;
  function &foo (){ //this is the right function
    global $a;
    return $a;
  }
  function boo (){ //no &
    global $b;
    return $b;
  }
  function &coo (){
    global $c;
    return $c+10; //expression
  }

  $x = &foo(); //binds $x to $a
  $x = 7;
  print ("a=$a "); // 7 - changed

  $y = &boo();
  $y = 5;
  print ("b=$b "); // 0 - unchanged

  $z = &coo();
  $z = 17;
  print ("c=$c");  // 0 - unchanged

?>