title: Why does rand() compile without including cstdlib or using namespace std?
body: <p>According to the book I'm reading, <code>rand()</code> requires <code>#include &lt;cstdlib&gt;</code> in C++<br>
  However, I am able to compile the following code that uses <code>rand()</code> without <code>#include &lt;cstdlib&gt;</code>  nor <code>using namespace std;</code> in Visual Studio 2015.<br>
  Why are these two not needed to compile? Should I include cstdlib?</p>
  
  <p>C++ Code:</p>
  
  <pre><code>#include &lt;iostream&gt;
  
  int main()
  {
      std::cout &lt;&lt; rand() &lt;&lt; std::endl;
  }
  </code></pre>