title: expressing hex value in 2's complement
body: <p>i have a string hex value, and i need to express it in 2's complement.</p>
  
  <pre><code>string hx = "FF00";
  </code></pre>
  
  <p>what i did is, converting it to binary:</p>
  
  <pre><code> string h = Convert.ToString(Convert.ToInt32(hx, 16), 2 );
  </code></pre>
  
  <p>then inverting it, but i couldn't use the <code>NOT</code> operator.</p>
  
  <p>is there any short way to invert the bits and then adding 1 (2's complement operation)?</p>