PHP subtraction problem

lunacyfoundme

Im getting a value of -5.8207660913467E-13 instead of 0 when I subtract two values. The two values are calculated values monetary but when echoed to screen seem to be the exact same. Ive tried converting them to cent and subtracting but with the same result. There must be a very slight difference in them but Im not sure how to resolve this. Any ideas what Im doing wrong?

Ross

How are you performing the subtraction? Posting the code you're using would help.

Have a read of How to deal with strange rounding of floats in PHP.

You probably want to use round.

lunacyfoundme

Ill have a look at that thanks. Got around the issue for the minute by converting the decimalised monetary amount to cents and using (int) cast to make sure the cent amount is a whole number. Not sure if its loses a cent here or there but its a general report so it doesnt have to that accurate.

Thanks.

democrates

I'd use round() first, (int) casting rounds down.


Also be careful of the rounding error window, eg:

107 * .21 = 22.47 rounds to 23
107 * .79 = 84.53 rounds to 85

so the sum of the parts is now greater than the whole...