title: Unknown value in Visual C++
body: <p>While doing some calculations in Visual Studio C++ I found the final value of <code>angle</code> to be <code>-1.#IND000000000000</code></p>
  
  <p>What does this value mean? Has it gone out of scope?
  Following is the code I was trying to implement <em>How do I calculate arc angle between two points on a circle?</em> from this formula <br> cos<sup>-1</sup> ((x<sub>1</sub>x<sub>2</sub> + y<sub>1</sub>y<sub>2</sub> + z<sub>1</sub>z<sub>2</sub>) / r<sup>2</sup>) as mentioned <a href="https://stackoverflow.com/a/2994683/603125">here</a></p>
  
  <p><strong>CODE</strong></p>
  
  <pre><code>double x = vec1X * vec2X;
  double y = vec1Y * vec2Y;
  double r = sqrt(((vec2X - originX) * (vec2X - originX))+((vec2Y - originY) * (vec2Y - originY)));
  angle = acos ((x + y) / r*r);
  </code></pre>
  
  <p>Sample values to reproduce error<br></p>
  
  <pre><code>vec1X = 91.094001770019531;
  vec1Y = 147.74990844726562;
  vec2X = 94.163322448730469;
  vec2Y = 187.93711853027344;
  originX = 136.79920959472656;
  originY = 223.69624328613281;
  </code></pre>