title: Print list of binary permutations
body: <p>What I am trying to do is print all the possibilities of a binary number n digits long. In other words, with a 4 digit number:</p>
  
  <pre><code>0001
  0010
  0100
  1000
  </code></pre>
  
  <p>..etc</p>
  
  <p>To be honest, I have no idea of where to even start with this (other than I figure I'd need to use a loop, and probably an array) so any pointers in the right direction would be appreciated.</p>