How to abbreviate/format php numbers, as on Youtube?

Question

Ex: 10000 turns 10k, 1000000 turns 1M and so on?

Well, I did it this way. If anyone has a better and more practical way, please let me know:

function abrevNmr($numero){     
        switch(strlen($numero)){
            case 1:
            case 2:
            case 3:
                    return $numero;
                break;
            case 4: 
                    $num = str_split($numero, 1);
                    return $num[0].($num[1] > 0 ? ','.$num[1] : null).'k';
                break;
            case 5:
                    $num = str_split($numero, 1);
                    return $num[0].$num[1].($num[2] > 0 ? ','.$num[2] : null).'k';
                break;
            case 6:
                    $num = str_split($numero, 1);
                    return $num[0].$num[1].$num[2].($num[3] > 0 ? ','.$num[3] : null).'k';
                break;
            case 7:
                    $num = str_split($numero, 1);
                    return $num[0].($num[1] > 0 ? ','.$num[1] : null).'mi';
                break;
            case 8:
                    $num = str_split($numero, 1);
                    return $num[0].$num[1].($num[2] > 0 ? ','.$num[2] : null).'mi';
                break;
        }
    }

It goes up to 99 million, because that’s more than enough for what I want.