Basic mathematics in PHP Simplexml

Question

The code below is in PHP and returns prices from a XML response file.

$price = $result->Items->Item->OfferSummary->LowestNewPrice->FormattedPrice; //lowest new price 
$listPrice = $result->Items->Item->Offers->Offer->OfferListing->Price->FormattedPrice; //list price

If I echo $price or $listPrice it works

I wish to get the difference between the two prices but I am getting NULL if I do

$savings = $listPrice - $price; or $savings = ($listPrice - $price);

Any assistance is welcome

Answer 1

You're most likely trying to subtract a string from a string. You need to convert the values to a numeric type. If you're working with prices, you'll probably want floating point numbers:

$price = floatval($result->Items->Item->OfferSummary->LowestNewPrice->FormattedPrice); //lowest new price 
$listPrice = floatval($result->Items->Item->Offers->Offer->OfferListing->Price->FormattedPrice); //list price

$savings = $listPrice - $price;