```
<?php
$a=[
    [
        "a"=>1,
        "b"=>2,
    ],
    [
        "c"=>1,
        "d"=>2,
    ],
];
echo key(reset($a));

```

result

```
a

```

I need it to return the first index of the array which is 0, but it return 'a'.
Do i using it wrong way?