title: making a copy for a variable
body: <p>Consider this piece of code:</p>
  
  <pre><code>int *a, *b;
  a = foo();
  if (a)
     b = a;
  a = bar();
  </code></pre>
  
  <p>The problem is, when <code>a</code> updates by calling <code>bar()</code>, <code>b</code> also updates. However I want to make a backup by using <code>b = a</code>. What is the problem then?</p>