cs193p Swift - key value coding error
<p>I can't believe I'm having a problem with the very first lecture! We are building a calculator (it is not at all functional as a calculator at this point). Mine was working just fine until the performOperation function was added. Now I'm getting "this class is not key value coding compliant" error. The thing is that, as far as I can see, my code EXACTLY replicates the code that he is using in the class. I must be missing something but I've checked roughly 50 times to find a difference and I can't find one. Help? It is crashing every time.</p>

<pre><code>import UIKit

class ViewController: UIViewController {

@IBOutlet weak var display: UILabel!

var userIsInTheMiddleOfTyping = false

@IBAction func touchDigit(sender: UIButton) {
    let digit = sender.currentTitle!

    if userIsInTheMiddleOfTyping {
        let textCurrentlyInDisplay = display.text!
        display.text = textCurrentlyInDisplay + digit
    } else {
        display.text = digit
    }

    userIsInTheMiddleOfTyping = true
}


@IBAction func performOperation(sender: UIButton) {
    userIsInTheMiddleOfTyping = false
    if let mathematicalSymbol = sender.currentTitle {
        if mathematicalSymbol == "π" {
            display.text = String(M_PI)
        }
    }
}

}
</code></pre>

<p>EDIT: Code format</p>