从String中的某个位置获取一个数字，然后将其用于计算

I'm trying to code a function that will do some mathematical operations. Here's an example:

function test($number){
    $result = 5 * $number[2];
    echo $result;
}

So if I enter a number "12345", I want to multiply the number at index 2 with 5. So in this case, I should be multiplying 5*3 and get 15.

But I always get 0. I found the error why I'm always getting 0. It's because $number[2] isn't working. So how do I get a number at a certain index and then calculate with it?

The problem is that you can get the number by index only of string not of int.

test("124"); // working
test(124); // not working

Possible solution is this:

function test($number){
    $number = "$number";
    $result = 5 * $number[2];
    echo $result;
}

test(124);