PHP 字符串转数组与数组转字符串

//数组按指定方式分割为字符串
$arr = array('Hello','World!','I','love','Shanghai!');
    
echo implode(" ",$arr);

//字符串按指定规则合并为数组
$string = "Hello World love Shanghai";

$arr = explode(" ", $pizza);

print_r($arr);