Q27. What is Navigation Controller.?Ans:- 
- Navigation related functionalities can be implemented by using UINavigationController.
- Navigation it’s use for go next view to next and back.(just like linking).
- UINavigationController take the navigation text as a back button title otherwise by default is Back as a text.
- If u want first view to second view then recommended to use for PushViewController, it is always work on left to right and automatically back also.
- popVIewController what he doing he romove/close current view and returns the parrent view means return the one that pushed the current view).
- when we required to remove view then we need to go for popViewController option and it will handle automatically by the navigationController and it works towards right to left.
- when we are working with navigation related application by default UINavigationController will handles pop operation(view going back).
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