关于“＆”在php中使用

Question

$arr1 = array(1);
arr2 = $arr1;
$arr2[0]++;//$arr1[0]=1,$arr2[0]=2

But the following code:

$arr1 = array(1);
$a =& $arr1[0];
$arr2 = $arr1;
$arr2[0]++;//$arr1[0]=2,$arr2[0]=2

When I add $a, the output is different! Why does this happen?

Answer 1

@JakubMatczak Thanks for your professional response.But I still have some question.

$arr1 = array(1, 2);
$a =& $arr1;
$arr2 = $arr1;
$arr2[0]++;
$arr2[1]++;

Why the result of $arr1 is array(1, 2) not array(2, 2)?