為什么二維數組索引加關聯形式里面的鍵不能用方括號只能用雙引號？例如?$res=array (
[0]=>array("id" => "28" ,"username"=> "admin" ,"password" => "admin" ,"age" => "270"),
[1]=>array("id" => "29", "username" => "admin", "password" => "admin" ,"age" => "270"));

??$res=array (
"0"=>array("id" => "28" ,"username"=> "admin" ,"password" => "admin" ,"age" => "270"),
"1"=>array("id" => "29", "username" => "admin", "password" => "admin" ,"age" => "270"));上面執行出來就是Parse error: syntax error, unexpected '[', expecting ')' 下面執行出來就對的