title: How can I distinguish between an unset float and one with a value of 0?
body: <p>I have a method that needs to do a different thing when given an unset float than a float with the value of 0. Basically, I need to check whether or not a variable has been, counting it  as set if it has a value of 0.</p>
  
  <p>So, <strong>what placeholder should I use as an unset value</strong> (nil, NULL, NO, etc) and <strong>how can test to see if a variable is unset</strong> without returning true for a value of 0?</p>