CODE EXAMPLE FOR SWIFT

string to double swift

let lessPrecisePI = Float("3.14")

let morePrecisePI = Double("3.1415926536")
let invalidNumber = Float("alphabet") // nil, not a valid number
//Unwrap the values to use them using if/let

if let cost = Double(textField.text!) {
    print("The user entered a value price of (cost)")
} else {
    print("Not a valid number: (textField.text!)")
}
//You can convert formatted numbers and currency using the NumberFormatter class.

let formatter = NumberFormatter()
formatter.locale = Locale.current // USA: Locale(identifier: "en_US")
formatter.numberStyle = .decimal
let number = formatter.number(from: "9,999.99")