Javascript math question...

[Ichinisan]

I'm sure this is really basic, but I've been messing around with parseInt, toInt, parseFloat, toString, etc and can't figure out what's happening here.

alert(3*19.95);

"59.849999999999994"

It should be "59.85" ...so what's with the bad math?

 

[sourceninja]

Ahh floating point. Yes, if you need accurate floating point, well good luck...

 

[Ken g6]

Floating point rounding error. http://support.microsoft.com/kb/42980

By the way, until recently, floating point was the only kind of number supported by JavaScript.

 

[janas19]

I want to know what floating point means! 😀

 

[KB]

I hate dealing with floating points in jscript. If I recall correctly I used this function to get the value I actually wanted:

alert(Round(3*19.95, 2));


function Round(value, decimals) {
    return (Math.round(value * Math.pow(10, decimals)) / Math.pow(10, decimals));
}

 

[Ichinisan]

I hate dealing with floating points in jscript. If I recall correctly I used this function to get the value I actually wanted:

alert(Round(3*19.95, 2));


function Round(value, decimals) {
    return (Math.round(value * Math.pow(10, decimals)) / Math.pow(10, decimals));
}

It's strange that this is rounding at all when I'm not dividing and it's a fairly small number without a lot of precision. Anyway, I had to do something similar to:

((3*1995)/100)

I would expect the extra division operation to increase the chances of a math problem...but this works for some reason.

 

[IHateMyJob2004]

A computer does nto represent 0.95 as 0.95 in memory. It uses something like 0.9444449.

If you want your output to be human readable, use String.format().