Converting String to Int with Swift

Basic Idea, note that this only works in Swift 1.x (check out ParaSara's answer to see how it works in Swift 2.x):

    // toInt returns optional that's why we used a:Int?
    let a:Int? = firstText.text.toInt() // firstText is UITextField
    let b:Int? = secondText.text.toInt() // secondText is UITextField

    // check a and b before unwrapping using !
    if a && b {
        var ans = a! + b!
        answerLabel.text = "Answer is \(ans)" // answerLabel ie UILabel
    } else {
        answerLabel.text = "Input values are not numeric"
    }

Update for Swift 4

...
let a:Int? = Int(firstText.text) // firstText is UITextField
let b:Int? = Int(secondText.text) // secondText is UITextField
...

You can use NSNumberFormatter().numberFromString(yourNumberString). It's great because it returns an an optional that you can then test with if let to determine if the conversion was successful. eg.

var myString = "\(10)"
if let myNumber = NSNumberFormatter().numberFromString(myString) {
    var myInt = myNumber.integerValue
    // do what you need to do with myInt
} else {
    // what ever error code you need to write
}

Swift 5

var myString = "\(10)"
if let myNumber = NumberFormatter().number(from: myString) {
    var myInt = myNumber.intValue
    // do what you need to do with myInt
  } else {
    // what ever error code you need to write
  }

Updated answer for Swift 2.0+:

toInt() method gives an error, as it was removed from String in Swift 2.x. Instead, the Int type now has an initializer that accepts a String:

let a: Int? = Int(firstTextField.text)
let b: Int? = Int(secondTextField.text)

myString.toInt() - convert the string value into int .

Swift 3.x

If you have an integer hiding inside a string, you can convertby using the integer's constructor, like this:

let myInt = Int(textField.text)

As with other data types (Float and Double) you can also convert by using NSString:

let myString = "556"
let myInt = (myString as NSString).integerValue