How to add right button in the navigation bar?

The Swift version of Vahan Babayan's answer, as you seem to use this language, is:

let rightButtonItem = UIBarButtonItem.init(
      title: "Title", 
      style: .Done, 
      target: self, 
      action: "rightButtonAction:"
)

self.navigationItem.rightBarButtonItem = rightButtonItem

The following method will be called on self:

func rightButtonAction(sender: UIBarButtonItem)

Note that all this can be set graphically using a Storyboard, by dragging a Bar Button Item to your Navigation Item and right-clicking to set a target-action.

---

A small update since Swift 3 and 4 are out: the compiler can now check selector names, preventing typos when setting up target-action programatically. So one should really use:

let rightButtonItem = UIBarButtonItem.init(
      title: "Title", 
      style: .Done, 
      target: self, 
      action: #selector(rightButtonAction(sender:))
)

You can add the following code to your B controller's viewDidLoad method.

UIBarButtonItem *rightButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Title" 
                                                                    style:UIBarButtonItemStyleDone 
                                                                    target:self 
                                                                    action:@selector(rightButtonAction:)];
self.navigationItem.rightBarButtonItem = rightButtonItem;