title: Objective-C: Different ways of declaring private variables. Any differences between them?
body: <p>I have thought of different ways of declaring private variables. I want to know whether there are any differences between them.<br/>
  First way:</p>
  
  <pre><code>//In .h file
  @interface DataExtract : NSObject
  {   
      @private
      double test;
  }
  </code></pre>
  
  <p>Second way:</p>
  
  <pre><code>//In .m file. test is not declared in .h file
  static double test;
  </code></pre>
  
  <p>Third way:</p>
  
  <pre><code>//In .m file. test is not declared in .h file
  double test;
  </code></pre>
  
  <p>Any help would be much appreciated. Thank you.</p>