title: error: ‘NULL’ was not declared in this scope
body: <p>I get this message when compiling C++ on gcc 4.3</p>
  
  <pre><code>error: ‘NULL’ was not declared in this scope
  </code></pre>
  
  <p>It appears and disappears and I don't know why. Why?</p>
  
  <p>Thanks.</p>