checking if a number is divisible by 6 PHP

$num += (6-$num%6)%6;

no need for a while loop! Modulo (%) returns the remainder of a division. IE 20%6 = 2. 6-2 = 4. 20+4 = 24. 24 is divisible by 6.

if ($variable % 6 == 0) {
    echo 'This number is divisible by 6.';
}:

Make divisible by 6:

$variable += (6 - ($variable % 6)) % 6; // faster than while for large divisors

if ($number % 6 != 0) {
  $number += 6 - ($number % 6);
}

The modulus operator gives the remainder of the division, so $number % 6 is the amount left over when dividing by 6. This will be faster than doing a loop and continually rechecking.

If decreasing is acceptable then this is even faster:

$number -= $number % 6;

So you want the next multiple of 6, is that it?

You can divide your number by 6, then ceil it, and multiply it again:

$answer = ceil($foo / 6) * 6;