$arr=array("a","b","c","d");

foreach ($arr as &$value) {

}
//$value=&arr[3];$value="d";

foreach ($arr as $key=>$value) {
  echo "
";
  var_dump($arr);

}

 the results are as follows 
array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
  [3]=>
  &string(1) "a"
}

array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
  [3]=>
  &string(1) "b"
}

array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
  [3]=>
  &string(1) "c"
}

array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
  [2]=>
  string(1) "c"
  [3]=>
  &string(1) "c"
}

 I would like to ask that $value=&arr [3] has been determined before the second foreache function; then the following 
 $value=$arr [0] in the first loop; whether it completely covers the first $value, 
 and why, and the last value is whether abcc, can be explained from the zval structure