title: Define integer (int); What's the default value?
body: <pre><code>int i;
  int data[5] = {0};
  data[0] = i;
  </code></pre>
  
  <p>What's the value in data[0]?</p>
  
  <p>Also, what's the meaning of this line?</p>
  
  <pre><code>if (!data[0]) { ... }
  </code></pre>