title: How big can a 64 bit unsigned integer be?
body: <p>I am quite clear about <a href="https://stackoverflow.com/questions/6003492/how-big-can-a-64bit-signed-integer-be">How big can a 64bit signed integer be?</a>
  Thanks to this question and its straightforward answers.</p>
  
  <p>So, according to that, could I say that an <code>unsigned int</code> can be 2^64 - 1, rather than 2^63 - 1?</p>
  
  <pre><code>2^63 - 1:    0111111111111111111111111111111111111111111111111111111111111111
  
  2^64 - 1:    1111111111111111111111111111111111111111111111111111111111111111
  </code></pre>
  
  <p>If and only if I got it correctly,  how can I detect an unsigned overflow? An overflow of a signed integer in two's complement representation would invade the highest bit position, returning a negative number. But how about this unsigned case? </p>