Math bug or user error?

[fooDigi]

Can someone tell me why i get this absurd number when doing simply addition and subtraction? thx

 

$charge_amount = 34.55;
$amount_paid = 179.99;
$order_total = 214.54;

// returns 2.84217094304E-14 ... should be zero
echo $charge_amount + $amount_paid - $order_total;

[Mark Baker]

Can someone tell me why i get this absurd number when doing simply addition and subtraction? thanks

Pay particular heed to the Warning on this page

 

 

[fooDigi]

k, so even though when i print the sum of $charge_amount and $amount_paid, it returns 214.54, and $order_total is 214.54, their internal values may not be as exact?? confusing, what would be the best and most accurate way to avoid this?

 

changing it to the following worked, but not sure if it is best...

echo round($charge_amount + $amount_paid,2) - $order_total;

 

also, i have been running this code for some time, and this is the first time this issue has arose...

[Mark Baker]

Depends what you math is for.

 

Simply use round or number_format to control the number of decimal place if you just want to echo the result.

If these are monetary values, then it's always a lot better to hold the values as an integer number of cents/pennies rather than a float dollars/pounds: doing all of your math using integers won't give any rounding errors.

Use the bc math functions, as the Warning message suggests

[fooDigi]

Thanks Mark, got it working...