title: cerr is undefined
body: <p>I have some problems, I'm getting these errors (marked in the code):</p>
  
  <ul>
  <li>identifier "cerr" is undefined</li>
  <li>no operator "&lt;&lt;" matches these operands</li>
  </ul>
  
  <p>Why?</p>
  
  <pre><code>#include "basic.h"
  #include &lt;fstream&gt;
  
  using namespace std;
  
  int main()
  {
  
      ofstream output("output.txt",ios::out);
      if (output == NULL)
      {
          cerr &lt;&lt; "File cannot be opened" &lt;&lt; endl;   // first error here
          return 1;
      }
  
      output &lt;&lt; "Opening of basic account with a 100 Pound deposit: "
          &lt;&lt; endl;
      Basic myBasic (100);
      output &lt;&lt; myBasic &lt;&lt; endl;   // second error here
  }
  </code></pre>