title: How to add to an NSDictionary
body: <p>I was using a <code>NSMutableArray</code> and realized that using a dictionary is a lot simpler for what I am trying to achieve.</p>
  
  <p>I want to save a key as a <code>NSString</code> and a value as an <code>int</code> in the dictionary. How is this done?  Secondly, what is the difference between mutable and a normal dictionary?</p>