Find out the nearest bigger multiple of (n) PHP

Question

I have a requirement where users are forced to choose the multiple of (n) quantity of a product.

The (n) value is set with each product that can be any number.

customer can only purchase the quantity of product in the multiple of (n) quantity set with product.

Suppose if (n) is 5 and user entered quantity as 4 and says Add to Cart. I have to add quantity of that product as 5 automatically.

and if user entered 6 as quantity then I have to add the 10 quantity of that product.

How I go about that?

I am not getting what logic should be applied here.

Answer 1

$entered_quantity = 6;
$suppose_n = 5;

$quantity = ceil($entered_quantity / $suppose_n) * $suppose_n;

echo $quantity;

prints 10

Answer 2

that's not php specific; what you wonna do is to compute.

ceiling(q / n) * n

where q is the user's quantity, n is the multiplicity