title: How to check for undefined value of a double?
body: <p>I am trying to figure out a way to check for a undefined value of a slope in which case it would be vertical. I have tried using <code>NULL</code> but that doesn't seem to work.</p>
  
  <pre><code>double Point::Slope(Point &amp;p2)
  {
     double slop = 0;
     slop = (y - p2.y) / (x - p2.x);
  
     if (slop == NULL)
     {
        slop = 10e100;
     }
  
     return slop;   
  }
  </code></pre>