Convert a strong to a 32-bit integer - curly braces is no longer supported

Question

I have a very old code that now needs to be made PHP 8 executable, unfortunately I'm stuck with what should be a simple task.

How can I solve the problem in line 17. array and string offset access syntax with curly braces is no longer supported.

//convert a string to a 32-bit integer
function StrToNum($Str, $Check, $Magic)
{
    $Int32Unit = 4294967296;  // 2^32

    $length = strlen($Str);
    for ($i = 0; $i < $length; $i++) {
        $Check *= $Magic;
        //If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), 
        //  the result of converting to integer is undefined
        //  refer to http://www.php.net/manual/en/language.types.integer.php
        if ($Check >= $Int32Unit) {
            $Check = ($Check - $Int32Unit * (int)($Check / $Int32Unit));
            //if the check less than -2^31
            $Check = ($Check < -2147483648) ? ($Check + $Int32Unit) : $Check;
        }
        $Check += ord($Str{$i});
    }
    return $Check;
}

My first thought is that you can use the Strig. Or the array accordingly defined before. Am I right there?

Update Solution: Changed ($Str{$i} to ($Str[$]}. Solved.