title: Dynamically format a float in a NSString
body: <p>Consider this:</p>
  
  <p><code>NSString *whatever=[NSString stringWithFormat:@"My float: %.2f",aFloat];</code></p>
  
  <p>This will round my <code>aFloat</code> to 2 decimal places when building the string <code>whatever</code></p>
  
  <p>Suppose I want the <code>2</code> in this statement to be assignable, such that, based on the value of <code>aFloat</code> I might have it show 2 or 4 decimal places. How can I build this into <code>stringWithFormat</code>?</p>
  
  <p>I want to be able to do this without an <code>if</code> that simply repeats the entire line for different cases, but rather somehow dynamically change just the <code>%.2f</code> portion.</p>