title: iOS: Use a boolean in NSUserDefaults
body: <p>When the <code>rootViewController</code> of my application is loaded, I want to be able to check whether or not the users login credentials have been saved to <code>NSUserDefaults</code>.</p>
  
  <p>Basically, when the user loads the application and he/she doesn't have her login credentials saved, a <code>modalAlertView</code> will be pushed and the user will be able to save their credentials appropriately. This saves those <code>UITextField</code> strings to a respective <code>NSUserDefault</code> object. However, is it possible, that when this saving is done, I can create an <code>NSUserDefault</code> object which is a boolean and change the value to a yes?</p>
  
  <p>Meaning that the boolean is already set to no, and when the user saves their login credentials, it also changes the boolean to a yes?</p>