I have coding about 3 dimensional array. I need a function to automatically check where the empty slot is, and then insert the empty array ($rhw[104][1][2]) values Class C.

The coding structure is,

```
$rhw[101][1][2] = "Class A";
$rhw[102][1][2] = "Class B";
$rhw[103][1][2] = "";

```

And i just can make like the coding below,

```
if (empty($rhw[103][1][2])) {
    echo "TRUE";
} else {
    echo "FALSE";
}

```

But there is already declared like --- if (empty($rhw[103][1][2])) ---
I dont know how to automatically check where the empty slot is (which is $rhw[103][1][2]).

Such as,

```
if (empty($rhw[][][])) {
    insert "Class C";
} else {
    echo "The slot has been fulfilled";
}

```

But it can not be proceed.

Thank you, guys! :)