title: ios app crash when calling a property with the underscore format
body: <p>I have declared a variable in .h:</p>
  
  <pre><code>@property (nonatomic, retain) NSString *var;
  </code></pre>
  
  <p>When i call a property variable using:</p>
  
  <pre><code> _var = sumthing;
  </code></pre>
  
  <p>the app crashes and when i call it as:</p>
  
  <pre><code> self.var = sumthing;
  </code></pre>
  
  <p>it works well.</p>
  
  <p>Is there any difference in these two scenarios?</p>
  
  <p>NOTE: I have not used <code>@synthesize</code> as it is not required to write this specifically. </p>