Php 未定义完整数组的偏移量，但vardump已满

我的PHP代码有一些问题

<?php
  if(!empty($_POST['IP_adress'])){
    $IP_adress = $_POST['IP_adress'];
    $block[4] = explode(".",$IP_adress);
    $i = 0;
    var_dump($block);
    for($i=0;$i<4;$i++){
      if ($block[$i]<0 || $block[$i]>255){//here is line 9
        $_SESSION['IP_error'] = "non-valid IP adress";
        header('Location: controle.php');
      }
    }
  }
?>

你能帮我吗

p、 抱歉语法和英语不好。法语母语在这里

在第5行中，您使用了$block[4]=explode.，$IP_address；这就是var_转储的输出告诉您的

您已经创建了一个关联数组，分解后的IP数组作为值存储在数组$block的键4处。要访问分解的IP字段，您可以将第5行修改为$block=explode.，$IP_address；或者将第9行修改为if$block[4][$i]255{.

是否应该是$block=explode.，$IP_address？

array(1) { [4]=> array(4) { [0]=> string(3) "255" [1]=> string(3) "255" [2]=> string(3) "255" [3]=> string(3) "255" } }

Notice: Undefined offset: 0 in /var/www/html/select.php on line 9

Notice: Undefined offset: 0 in /var/www/html/select.php on line 9

Notice: Undefined offset: 1 in /var/www/html/select.php on line 9

Notice: Undefined offset: 1 in /var/www/html/select.php on line 9

Notice: Undefined offset: 2 in /var/www/html/select.php on line 9

Notice: Undefined offset: 2 in /var/www/html/select.php on line 9

Notice: Undefined offset: 3 in /var/www/html/select.php on line 9

Notice: Undefined offset: 3 in /var/www/html/select.php on line 9

[output errors][1]