A small mistake that is easy to overlook, have you ever made it?

foreach array value modification

/**
 * Note the difference in foreach values ​​
*/
$arr = array(1,2,3,4);

echo "foreach traverses array 1: ";
foreach( $arr as $val) {
 $val = $val*2;
}

var_dump($arr);

echo "foreach traverses array 2: ";
foreach( $arr as &$val) {
 $val = $val*2;
}

var_dump($arr);
/*end of php*/