title: what does Error "Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)" mean?
body: <p>I got this error:</p>
  
  <blockquote>
    <p>Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)</p>
  </blockquote>
  
  <p>How can I solve this? The code works normally, but in the calculator when I click the only equal button, it gives that error.</p>
  
  <pre><code>@IBAction func equals(sender: AnyObject) {
  
      secondNumber = Screen.text!.toInt()!  // here it shows an error which is "Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)"
  
      if operation == "+"{
          result = firstNumber + secondNumber
      }
      else if operation == "-" {
          result = firstNumber - secondNumber
      }
      else if operation == "x" {
          result = firstNumber * secondNumber
      }
      else {
          result = firstNumber / secondNumber
      }
      Screen.text = "\(result)"
  }
  </code></pre>