title: addObject to NSArray in Objective-C
body: <p>How to addObject to NSArray using this code? I got this error message when trying to do it.</p>
  
  <pre><code>NSArray *shoppingList = @[@"Eggs", @"Milk"];
  NSString *flour = @"Flour";
  [shoppingList addObject:flour];
  shoppingList += @["Baking Powder"]
  </code></pre>
  
  <p>Error message</p>
  
  <pre><code>/Users/xxxxx/Documents/iOS/xxxxx/main.m:54:23: No visible @interface for 'NSArray' declares the selector 'addObject:'
  </code></pre>