Validate check digit 11 (mod 11) using PHP

Question

How to validate NHS number using check digit 11 (mod 11) using PHP.

After a long search on the internet trying to find a function that I can use to validate check digit 11 (mod 11) number, I couldn't find so I end up developing one myself and share it here. I hope someone my find it useful.

Answer 1

The code with comments:

###### Check Digit 11 Modulus
function mod11($nhs_no){
    //Get Last Number
    $checkDigit = (int)substr($nhs_no, -1);
    //Get Remaining Numbers
    $numbers = substr($nhs_no, 0, -1);  
    // Sort Numbers Into an Array
    $numbers_array = str_split($numbers);
    //Define the base for the weights
    $base=2;
    // Multiply the weights to the numbers
    $numbers_array_reversed =  array_reverse($numbers_array);
    foreach($numbers_array_reversed as $number){$multiplier[$number.'x'.$base]=(float)$number * $base;$base++;}
    //Get the total sum
    $sum =(float) array_sum($multiplier);
    $modulus = 11;
    // Divide the sum by check digit 11
    $divider = (float)($sum / $modulus);
    // Get the remainder
    $remainder = (int)(($divider - (int)$divider)*$modulus);
    // Check if the remainder is matching with the last check digit
    $results = (int) ($modulus-$remainder);
    // Return true or false 
    return ($results == $checkDigit ? true : false);
}