[Solved] PHP Calculation – Modulus 10 check digit generation [closed]

by


In case someone gets to the question wondering how to use modulus or ‘getting the rest of a division’ (%):

echo 5 % 3; // outputs 2

(You can take a look at a step-by-step output after this first part)

This is the commented function:

function func_name($docnum){

    // make sure there is just numbers in $docnum
    $docnum = preg_replace("/[^0-9]/","",$docnum);      

    // change order of values to use in foreach
    $vals = array_reverse(str_split($docnum));

    // multiply every other value by 2
    $mult = true;
    foreach($vals as $k => $v){
        $vals[$k] = $mult ? $v*2: $v;
        $vals[$k] = (string)($vals[$k]);
        $mult = !$mult;
    }

    // checks for two digits (>9)
    $mp = array_map(function($v){
        return ($v > 9) ? $v[0] + $v[1] : $v;
    }, $vals);

    // adds the values
    $sum = array_sum($mp);

    //gets the mod
    $md = $sum % 10;

    // checks how much for 10
    $result = 10 - $md;

    // returns the value
    return $result;
}

Some test runs:

$docnum = 5843;
echo func_name($docnum);

Output:

8

$docnum = 1111;
echo func_name($docnum);

Output:

4

$docnum = '-5a84fadsafds.fdar3';
echo func_name($docnum);

Output:

8

$docnum = 4321;
echo func_name($docnum);

Output:

6

This codes outputs the steps…

$docnum = '-5a84fadsafds.fdar3';

echo 'Original Value: ';
print_r($docnum);
echo '<hr>';

$docnum = preg_replace("/[^0-9]/","",$docnum); 

echo 'Numbers only: ';
print_r($docnum);
echo '<hr>';

$vals = array_reverse(str_split($docnum));

echo 'Reversed Value: ';
print_r($vals);
echo '<hr>';

$mult = true;
foreach($vals as $k => $v){
    $vals[$k] = $mult ? $v*2: $v;
    $vals[$k] = (string)($vals[$k]);
    $mult = !$mult;
}

echo 'After mult.: ';
print_r($vals);
echo '<hr>';

$mp = array_map(function($v){
    return ($v > 9) ? $v[0] + $v[1] : $v;
}, $vals);

echo 'Checked for >9: ';
print_r($mp);
echo '<hr>';

$sum = array_sum($mp);

echo 'All values together: ';
print_r($sum);
echo '<hr>';

$md = $sum % 10;

echo 'Mod: ';
print_r($md);
echo '<hr>';

$result = 10 - $md;

echo 'Final result: ';
print_r($result);
echo '<hr>';

Output:

Original Value: -5a84fadsafds.fdar3
Numbers only: 5843
Reversed Value: Array ( [0] => 3 [1] => 4 [2] => 8 [3] => 5 )
After mult.: Array ( [0] => 6 [1] => 4 [2] => 16 [3] => 5 )
Checked for >9: Array ( [0] => 6 [1] => 4 [2] => 7 [3] => 5 )
All values together: 22
Mod: 2
Final result: 8

Read more about things used in the code:

As suggested by @Floris, you can replace the double-digit sum part with modulus 9, so instead of

$mp = array_map(function($v){
        return ($v > 9) ? $v[0] + $v[1] : $v;
    }, $vals);

you would have

$mp = array_map(function($v){
        return $v % 9;
    }, $vals);

and still keep the same output…

6

solved PHP Calculation – Modulus 10 check digit generation [closed]