title: What is the difference between UIView and UIViewController?
body: <p>I need a detailed explanation on the following:</p>
  
  <p>What do we use a <code>UIViewController</code> for?
  What is the use of it?</p>
  
  <p>I have a class that looks like the following:</p>
  
  <pre><code>class one
  {
      UINavigationController *nav = ...;
  
      two *secondObject = ...;
  
      // By use of it, I have push the new view class two//ok
  }
  class two
  {
   ...
  }
  </code></pre>
  
  <p>How can I use <code>secondObject</code> in the class <code>one</code>?</p>
  
  <p>What is the class hierarchical start from the window?</p>