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EAN13 Barcode Check Digit with PHP

EAN13 is a barcode format. It consists of 12 numbers which you will generally have a range assigned to you. The 13th digit is called the check digit and is formulated by loooking at the other 12 digits. The purpose of the check digit is to ensure that the number is being read correctly as if any of the numbers do not match up, the check digit will not validate.

If you need to create check digits in PHP, here is my handy function:

PLAIN TEXT

PHP:

function ean13_check_digit($digits){
//first change digits to a string so that we can access individual numbers
$digits =(string)$digits;
// 1. Add the values of the digits in the even-numbered positions: 2, 4, 6, etc.
$even_sum = $digits{1} + $digits{3} + $digits{5} + $digits{7} + $digits{9} + $digits{11};
// 2. Multiply this result by 3.
$even_sum_three = $even_sum * 3;
// 3. Add the values of the digits in the odd-numbered positions: 1, 3, 5, etc.
$odd_sum = $digits{0} + $digits{2} + $digits{4} + $digits{6} + $digits{8} + $digits{10};
// 4. Sum the results of steps 2 and 3.
$total_sum = $even_sum_three + $odd_sum;
// 5. The check character is the smallest number which, when added to the result in step 4, produces a multiple of 10.
$next_ten = (ceil($total_sum/10))*10;
$check_digit = $next_ten - $total_sum;
return $digits . $check_digit;
}