title: How to use static variable(BOOL) in Objective C
body: <p>I am from C# background, and I am having a hard time in figuring out about how to use a static variable(BOOL in my case) in Objective C.
  My questions are: </p>
  
  <ol>
  <li>Where should I declare my static variable. </li>
  <li>How can I access(set its value) from another class.</li>
  <li>Do I need to use extern keyword.</li>
  </ol>