title: Expression result unused -wunused-value in objective-c
body: <p>I'm not sure how to fix this, the error says "expression result unused -wunused-value." How would I fix this?</p>
  
  <p>Here's the code:</p>
  
  <pre><code>[self addChild: hero];
      screenWidth/2, screenHeight/10;
  </code></pre>