I'm trying to sort an array,but it doesn't work the way I want to.

My code is as follows.

```
<?php
$classroom = array("4/10","4/2","4/1","4/11","5/2","1/2","5/1","5/10","5/12");
sort($classroom);
print_r($classroom);
?>

```

The result is:

```
Array ( [0] => 1/2 [1] => 4/1 [2] => 4/10 [3] => 4/11 [4] => 4/2 [5] => 5/1 [6] => 5/10 [7] => 5/12 [8] => 5/2 )

```

I would like to sort it to be:

```
 1/2,4/1,4/2,4/10,4/11,5/1,5/2,5/10,5/12

```

I'm quite new to sort functions. Would you please give me an example of using usort?