How this code works?

Question

<?php
$a = '1';
$b = &$a;
$b = "2$b";
echo "$a , $b";
?>
Its printing 21 , 21. How?

Answer 1

& - is passing by reference. So, in this case variable $b contain address of $a, but not it's value. When you are change value of $b - really you change value of $a.

Answer 2

its 10
add 7 and 3

Answer 3

Oh I get it. So $b is actually copy of $a because it points same address. Thanks.

Answer 4

on row 3 "2$b" you just concatenate/merge the two values. at the moment $b = 1 -> 21