title: 2's complement example, why not carry?
body: <p>I'm watching some great lectures from David Malan (<a href="http://academicearth.org/lectures/binary-numbers-programming-languages-linux" rel="noreferrer">here</a>) that is going over binary. He talked about signed/unsigned, 1's compliment, and 2's complement representations. There was an addition done of 4 + (-3) which lined up like this:</p>
  
  <pre><code>0100
  1101 (flip 0011 to 1100, then add "1" to the end)
  ----
  0001
  </code></pre>
  
  <p>But he waved his magical hands and threw away the last carry. I did some wikipedia research bit didn't quite get it, can someone explain to me why that particular carry (in the 8's ->16's columns) was dropped, but he kept the one just prior to it?</p>
  
  <p>Thanks!</p>