title: check NSString for same character twice
body: <p>I'd like to check a UITextfield to make sure it doesn't contain a second decimal. How do I check a NSString for a second decimal?</p>
  
  <p>Really what I'd like to do is present a uitextfield and have just the number pad and make it so if the user presses 1 2 3 4 5 6 7 8 9 it shows up as "$1,234,567.89" however I run into issues converting the string to a float value and it rounding the result... but if I can just make sure that the user doesn't type 2 decimals I'll be good also.</p>