How do I explain this inconsistency ?

Hi there ! <img src="{SMILIES_PATH}/icon_e_biggrin.gif" alt=":D" title="Very Happy" />

I'm no big connoisseur in trigonometry but I had to dip into it a little in order to generate a laser for my Run N' Gun shooter. I've managed to have my laser working but I've been puzzled by one small inconsistency I can't explain...

(I've simplified the CapX and you can download it here : mediafire.com

(to generate a laser you have to hold an arrow or more and use the left click)

See, I have a debug box. When I add into my debug box Cos(270) it writes 0 as expected. Also Sin(270) writes -1.

So that's good.

But when I try to concatenate Cos(270)&" / "&Sin(270) the cosinus is wrong. It gives a figure veeeeery small but not nul. So it writes something like "-1.8369701987210297e-16 // -1" instead of "0 // -1".

Is it because of the cosinus ?

Or because of the concatenation ?

More importantly, can this mess up my computation for the laser's width in any way ? (line 27-28 of the Event Sheet 1)

Thanks in advance for taking the time to reassure me <img src="{SMILIES_PATH}/icon_e_smile.gif" alt=":)" title="Smile" />

Best regards

Why are you using strings for math?

What do you mean ?

I can usually concatenate figures without problem

Well to start it's an extra step to convert strings into numbers, and then there's bound to be issues with the conversion, which could vary widely between browsers.

I'm converting a number into a string, sure, but that doesn't explain why Cos(270°) becomes this weird number when it's not alone. 0 converted into a string should still be "0", right ?

Cos(270°) should always be strictly equal to zero... unless I don't understand cosinuses well (which is a possibility).

Could be 0, could be null.

It depends on the browser, and how it's setup to handle it.

That's the problem with floating point arithmetic. There's nothing you can do about it, you just have to deal with it. However, a number like -1.8369701987210297e-16 is so small that you won't ever notice anything visually... so you might as well consider it to be 0.

Yeah, the value is the real issue.

Sorry I'm just off on the strings.

That's like saying eggs+flour+milk+sugar=cookies

If you want to force the debug text to be more readable, I guess you could always do something like rounding the value to 5 or 6 decimals (or whatever number you deem significant).

example for 5 decimals :

Smaller values will then always be equal to 0.

Oh, it's just text.

Well, nevermind all I said.

Ok, thanks for your explanation you two

As long as it's not messing the calculations, it's ok. I'll use the rounding trick if I want a figure to appear in a debug log from now on.

Cheers and thanks again