Can you append strings to variables in PHP?

Why does the following code output 0?

It works with numbers instead of strings just fine. I have similar code in JavaScript that also works. Does PHP not like += with strings?

    $selectBox = '';
    for ($i=1; $i<=100; $i++)
    {
        $selectBox += '' . $i . '';
    }
    $selectBox += '';

    echo $selectBox;

?>

Answer

This is because PHP uses the period character . for string concatenation, not the plus character +. Therefore to append to a string you want to use the .= operator:

for ($i=1;$i<=100;$i++)
{
    $selectBox .= '' . $i . '';
}
$selectBox .= '';