Subtraction bug?

GDevelop general Bugs reports
1

I made a simple subtraction operation like this:

A=0.5
B=0.35
A-B=0.1500000000002 (wrong)
this should be 0.15

For comparison, I made a similar operation:

A=0.5
C=0.15
A-C=0.35 (right)

Is this a bug? Hope this gets fixed soon.

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GDevelop version : 5.0.138

2

tl;dr That’s due to how computers stores non-integer numbers (floats) and do math on them, and this cannot be fixed.

3

oh. maybe if I SubStr 0,150000000… to 4 letter (0,15) it will be correct. but I’m not sure.

4

If you know you only want 2 decimals, you could always use the roundTo() expression, it lets you round to a specific decimal point, so it’d be roundTo(yourmathhere,2).

5

Yes maybe roundTo or SubStr. I’m affraid if roundTo I will get 0,2.
So I try to multiply it with a large number , like 1000000000.
then do the subtraction to avoid the error.
(0.5x1000000000)-(0.35x1000000000)
then divide the result with 1000000000 again.
Maybe it work.

6

Can you also multiply by 100, use the floor function and divide by 100?
Or something using the floor function.?

7

Might be worth looking into the toFixed? There should be a handy extension for is.