一路很纠结的php面试题

一道很纠结的php面试题

$a = 1;$b = 'a';$a = $b++; //$a = 'a'    //$b = 'b'$b = $a++;      //$b = 'a'//$a = 'b'$c = set($a).$b;//$c = 3.'a'//$c = 3aecho $c;function set($a=2,$b=3){global $a; //$a = 'b'    $c = &$a;                $a += $b++;  //$a = 'b' + 3//$a = 3//$c = 3   return $c;}