title: Pass-by-value argument in message expression is undefined
body: <p>I'm developing an iPhone application and I getting that warning at method:</p>
  
  <pre><code>NSNumber *latitudeValue;
  NSNumber *longitudeValue;
  
  [self obtainLatitude:latitudeValue longitude:longitudeValue];
  </code></pre>
  
  <p>The method is declared as follows:</p>
  
  <pre><code>- (void) obtainLatitude:(NSNumber *)latitudeValue longitude:(NSNumber *)longitudeValue {
  
      NSNumberFormatter * f = [[NSNumberFormatter alloc] init];
      [f setNumberStyle:NSNumberFormatterDecimalStyle];
  
      latitudeValue = [f numberFromString:[latitude.text stringByReplacingOccurrencesOfString:@"," withString:@"."]];
      longitudeValue = [f numberFromString:[longitude.text stringByReplacingOccurrencesOfString:@"," withString:@"."]];
  
      [f release];
  }
  </code></pre>
  
  <p>As you can see, I'm trying to calculate <code>latitudeValue</code> and <code>longitudeValue</code> calling <code>obtainLatitude:longitude:</code> but I'm doing something wrong.</p>
  
  <p>How can I fix that error?</p>