When trying to make a countdown by 0.10 it prints wrong thing

Question

I'm trying to make a countdown timer for iOS and when I try to make it go down by 0.10 and when I run the program it after like 8.2, 8.1, it starts printing like this 7.900000000, 7.800000012 something like this.

Here what it prints

And also it's supposed to stop at 0 but

stops here

But it works perfectly when making it go down by 0.25, or .5 or 1.

Here is my code.

var seconds = 10.0
var timer = Timer()

@IBAction func startPressed(_ sender: Any) {
    startBtn.isHidden = true
    clickedTxt.isHidden = false
    numClicked.isHidden = false
    tapView.isEnabled = true
    timerTxt.isHidden = false
    secs.isHidden = false

    timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(ViewController.counter), userInfo: nil, repeats: true)
}

func counter()
{
    if(seconds > 0.0)
    {
        seconds -= 0.1
        secs.text = "\(seconds)"
    } else {
        timer.invalidate()
    }
}

Read http://stackoverflow.com/questions/588004/is-floating-point-math-broken?s=1|16.6051 — rmaddy, Apr 20 '17 at 01:22

score 1 · Accepted Answer · edited Jul 01 '22 at 08:01

1

You're seeing an effect of the way floating point numbers are formatted, essentially. And you can read more about that in the other question rmaddy pointed you to.

I suspect you mostly want to format that label nicely. In that case you can do something like:

secs.text = String(format:"%.1f", secs)

where you replace ".1" with however many places after the decimal you want.

edited Jul 01 '22 at 08:01

Glorfindel

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answered Apr 20 '17 at 01:31

Aaron Golden

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This solves the output issue, but it doesn't address the problem of stopping at `0`. – vacawama Apr 20 '17 at 01:41
1

Instead of testing whether it is greater than 0.0, test whether it is greater than the error value you are able to tolerate. Something like `if (seconds > 0.0001)`. – Price Ringo Apr 20 '17 at 01:56
Thank you Aaron Golden and Price Ringo , It works now. – Ashot Gharibyan Apr 20 '17 at 02:26
Aaron is it like the set precision in c++?? – Ashot Gharibyan Apr 20 '17 at 02:26

When trying to make a countdown by 0.10 it prints wrong thing

1 Answers1