Php quotation symbols & Why is the problem 3 / 2 / 2?

php, give me an explanation

$arr = array(3,2,1);
foreach($arr as &$val){}
foreach($arr as $key => $val) {
}

print_r($arr);
// 3 2 2
Array
(
    [0] => 3
    [1] => 2
    [2] => 2
)
Php
Mar.09,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1ea20fb-1ba6.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1ea20fb-1ba6.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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