title: Implement double sqrt(double x) in C++
body: <p>Implement <code>double sqrt(double x)</code> in C++ without using std library.</p>
  
  <p>This is a facebook interview question I saw here. <a href="http://www.glassdoor.com/Interview/Implement-double-sqrt-double-x-in-C-QTN_87210.htm" rel="nofollow">http://www.glassdoor.com/Interview/Implement-double-sqrt-double-x-in-C-QTN_87210.htm</a>
  Any other good idea about this?...</p>
  
  <p>!!!Edited.!!!(without using std library.)</p>