title: When Int overflow cause IOS app crash, how can I remark it
body: <p>My app have to use <code>int</code> to do some multiplication, it is easy to meet two fairly big numbers' multiplication.</p>
  <p>Of course it will crash. And how can I remark some bool value. Just like every time before we'll quit the app, we <code>saveData</code> in the <code>AppDelegate.swift</code>'s function:</p>
  <pre><code>func applicationWillTerminate(application: UIApplication) {
          // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
  }
  </code></pre>