Math Function Help

[Anon]

I am currently working on a weight calculator that I will utilize in my shipping function.

I have managed to slop something together that will work for up to a QTY of 24 items.

---

$qty = 23; //used for testing purposes will be based on the qty of items selected.

$bottleweight = 3; //fixed bottle weight

$shipweight = range(1,8); //weight based on package weight which varies by qty

if($qty <3){
$total = $bottleweight $qty + $shipweight[0];
echo "$total";
} elseif($qty > 2 && $qty < 7){
$total = $bottleweight $qty + $shipweight[1];
echo "$total";
} elseif($qty > 6 && $qty < 9){
$total = $bottleweight $qty + $shipweight[2];
echo "$total";
} elseif($qty >8 && $qty < 13){
$total = $bottleweight $qty + $shipweight[3];
echo "$total";
} elseif($qty >12 && $qty < 15){
$total = $bottleweight $qty + $shipweight[4];
echo "$total";
} elseif($qty >14 && $qty < 19){
$total = $bottleweight $qty + $shipweight[5];
echo "$total";
} elseif($qty >18 && $qty < 21){
$total = $bottleweight $qty + $shipweight[6];
echo "$total";
} elseif($qty > 20 && $qty < 25){
$total = $bottleweight $qty + $shipweight[7];
echo "$total";
}

If anyone could please give me some pointers I would greatly appreciate it, I have been unable to come up with a formula, and this works fine for obviously up to 24 items.

Thanks all,

John

[Anon]

It looks to me like the change in $qty alternates between 3 and 5. If this is generally true (that is, it's true for quantities larger than 25,) then you can use something like:

if ( ( ($qty + 1) % 8 ) < 3 ) {

they ordered 0,1,2 or

(8 * y) + 0, 1, or 2 for

some y

$total = $bottleweight * $qty + $shipweight[floor($qty/8)];
} else {

they ordered 3,4,5,6,7 or

(8 * y) + 3,4,5,6, or 7 for

some y

$total = $bottleweight * $qty + $shipweight[floor($qty/8)+1];
}

I suspect, though, that $shipweight[] varies with packaging in the following way- you can either put the bottles in a 2 pack, or in a 6 pack. Every 2 pack weighs $twopack and every 6 pack weighs $sixpack. In that case, what you really want to do is maximize the number of 6 packs you use with the proviso that you will use a 2 pack for 1 or 2 bottles.

If that's the case, you want something like:

$total = $bottleweight $qty;
$total += floor($qty/6) $sixpack;
$total += ($qty % 6) < 3?$twopack:$sixpack;

I think that says, $total starts as the weight of all of the bottles, then $total gets the number of six packs times the weight of a sixpack added, then if there are one or two bottles $total gets a $twopack's weight, otherwise it gets a $sixpack's weight added.

-- Matt

[Anon]

Matt your the man of the hour, I need to really kick myself in the foot for not noticing that these are shipping in 2packs and 6 packs, kind scary that you hit the nail on the head.

Thanks again for your help, works like a charm and greatly appreciated!!!

John