title: Using the result of an assignment as a condition without parentheses
body: <p>I have this inside a custom UIActionSheet class</p>
  
  <pre><code>if (otherButtonTitles != nil) {
      [self addButtonWithTitle:otherButtonTitles];
      va_list args;
      va_start(args, otherButtonTitles);
      NSString * title = nil;
      while(title = va_arg(args,NSString*)) { // error here
          [self addButtonWithTitle:title];
      }
      va_end(args);
  }
  </code></pre>
  
  <p>I have this error</p>
  
  <p><strong>! using the result of an assignment as a condition without parentheses</strong></p>
  
  <p>pointing to this line</p>
  
  <pre><code>while(title = va_arg(args,NSString*)) {
  </code></pre>
  
  <p>why is that?</p>
  
  <p>thanks.</p>