Question

I have an customer invoice table in my MySQL database with a DECIMAL(10,2) field called price.

When fetching these values in php and calculating a sum amount,

ex: in the script

$totalAmount = 0; // initialised them to 

   while(records){              

       $amount = $inv_amount - ($pay_amount + $onamount); //float i guess. 2.22, 14.22
       $totalAmount = $totalAmount + $amount; //float i guess. 2.22, 14.22 ..etc

    }

when echo $totalAmount; it has a slight error in the final amount 0.01 however when dealing which large datasets around 20,000 this error becomes very considerable such as 200+

what is the safest way to do this when dealing with prices and such with these numbers in PHP? Or will I end up with potential rounding errors and things like that which are common when working with floating point data types?

is using

round 
number_format

is the most suitable solution for this type of a financial application ?

Answer 1

Indeed, floating point numbers are not precise.
Either calculate in cent (multiply by 100 and calculate in integers), or calculate in strings using BC Math.