Convert Kelvin into Celsius in Swift

Question

I'm trying to retrieve the temperature from the users current location.

I am using the API from OpenWeatherMap. The problem is, they provide the temperature in Kelvin as default, and I would like it in Celsius.

I understand that I just need to subtract 273.15 from the kelvin value....? But i'm struggling to figure out where to do that.

My code for setting my labels:

var jsonData: AnyObject?

func setLabels(weatherData: NSData) {

    do {

        self.jsonData = try NSJSONSerialization.JSONObjectWithData(weatherData, options: []) as! NSDictionary

    } catch {
        //handle error here

    }

    if let name = jsonData!["name"] as? String {

        locationLabel.text = "using your current location, \(name)"

    }

    if let main = jsonData!["main"] as? NSDictionary {
        if let temperature = main["temp"] as? Double {

            self.tempLabel.text = String(format: "%.0f", temperature)

        }

    }

}

Can anyone help me get this right please, as I'm really not sure where to start, thanks.

Let me know if you need to see more of my code.

Answer 1

if let kelvinTemp = main["temp"] as? Double {
    let celsiusTemp = kelvinTemp - 273.15
    self.tempLabel.text = String(format: "%.0f", celsiusTemp)
}

or simply

self.tempLabel.text = String(format: "%.0f", temperature - 273.15)