php获取数组第一个元素下标的两种方法

<?php
header("Content-type:text/html;charset=utf-8");
$arr=array("a"=>"1","b"=>"","c"=>"2","d"=>0,"e"=>"blue");
echo "原数组：";
var_dump($arr);
$keys=array_keys($arr);
echo "键名数组：";
var_dump($keys);
echo "原数组第一个元素的下标为：".$keys[0] ;
?>

<?php
header("Content-type:text/html;charset=utf-8");
$arr=array("a"=>"1","b"=>"","c"=>"2","d"=>0,"e"=>"blue");
echo "原数组：";
var_dump($arr);
echo "数组第一个元素的下标为：".key($arr) ;
?>