title: replace value of a NSString
body: <p>I am trying to replace the name of the month in an NSString with that of its two digit numerical value, e.g. "January"=>"01", "February"=>"02". The approach I am using is as follows:</p>
  
  <pre><code>if (mois==@"january") { mois=@"01";}   
  if (mois==@"February") { mois=@"02";}
  </code></pre>
  
  <p>...but it is not working. How do I go about making this replacement?</p>