title: Value assigned by double default constructor in c++
body: <p>I have this variable:
  <code>std::map&lt;std::string, double&gt; courses;</code></p>
  
  <p>And I'd like to print it if it has a value assigned for some key. So my keys are strings, so I want something like:</p>
  
  <pre><code>std::cin &gt;&gt; mystring;
  if (!(courses[mystring] == x)) std::cout &lt;&lt; courses[mystring] &lt;&lt; std::endl;
  </code></pre>
  
  <p>but I don't know what to make x. Any ideas?</p>