title: concatenate char array in C
body: <p>I have a a char array:</p>
  
  <pre><code>char* name = "hello";
  </code></pre>
  
  <p>I want to add an extension to that name to make it</p>
  
  <pre><code>hello.txt
  </code></pre>
  
  <p>How can I do this?</p>
  
  <p><code>name += ".txt"</code> won't work</p>