title: Convert NSString to NSDecimalNumber
body: <p>In my Core Data model, "amount" is an attribute in entity "Tracking".  How do I convert amount to NSDecimalNumber throughout the code?  I'm sure someone with more experience can do this in 3 minutes where I have been looking at it for days.</p>
  
  <pre><code>- (IBAction)save {
  if (![amount.text isEqualToString:@""]) {
  Tracking *tracking = [NSEntityDescription insertNewObjectForEntityForName:@"Tracking"
                                                 inManagedObjectContext:self.managedObjectContext];
  
      NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
      NSEntityDescription *weightEntity = [NSEntityDescription entityForName:@"Tracking" inManagedObjectContext:self.managedObjectContext];
      [fetchRequest setEntity:weightEntity];
      NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"timestamp" ascending:NO];
      [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
  
      NSError *error = nil;
      NSArray *result = [self.managedObjectContext executeFetchRequest:fetchRequest error:&amp;error];
  
      Tracking *person = [result objectAtIndex:0];
  
      NSLog(@"%@",person.date);
  
          NSDate *date = [NSDate date];
      NSDateFormatter *dateFormat = [[NSDateFormatter alloc]init];
      [dateFormat setDateFormat:@"MMM dd, yyyy"];
  
      NSString *dateString = [dateFormat stringFromDate:date];
      //NSString *dateString = @"Jan 13 2013";
      //Tracking *track = [self.fetchedResultsController objectAtIndexPath:nil];
  
  tracking.note = note.text;
  tracking.amount = amount.text;
  tracking.title = [segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex];
  tracking.date = dateString;
  tracking.timestamp = date;
  
          if (![person.date isEqualToString:dateString]) {
  
          if ([[segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex] isEqualToString:@"Food/Drink"]) {
              tracking.pic = @"Drink";
              tracking.total = [NSString stringWithFormat:@"%.2f", 0.00 - [amount.text floatValue]];
              NSLog(@"%f",[person.total floatValue]);
              NSLog(@"%f", [amount.text floatValue]);
              //tracking.total = @"1000.00";
          }
          else if ([[segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex] isEqualToString:@"Other"]) {
              tracking.total = [NSString stringWithFormat:@"%.2f",0.00 - [amount.text floatValue]];
              tracking.pic = [segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex];
  
          }
  
          else {
              tracking.pic = [segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex];
              tracking.total = [NSString stringWithFormat:@"%.2f",0.00 + [amount.text floatValue]];
          }
  
      }
  
      else {
  
  
          if ([[segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex] isEqualToString:@"Food/Drink"]) {
              tracking.pic = @"Drink";
              tracking.total = [NSString stringWithFormat:@"%.2f",[person.total floatValue] - [amount.text floatValue]];
              NSLog(@"%f",[person.total floatValue]);
              NSLog(@"%f", [amount.text floatValue]);
      //tracking.total = @"1000.00";
              }
          else if ([[segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex] isEqualToString:@"Other"]) {
              tracking.total = [NSString stringWithFormat:@"%.2f",[person.total floatValue] - [amount.text floatValue]];
              tracking.pic = [segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex];
  
          }
  
          else {
              tracking.pic = [segmentedChoice titleForSegmentAtIndex:segmentedChoice.selectedSegmentIndex];
              tracking.total = [NSString stringWithFormat:@"%.2f",[person.total floatValue] + [amount.text floatValue]];
  
          }
      }
  
  NSLog(@"\n Title: %@ \n Amount: %@ \n Note: %@ \n Date: %@ \n Picture: %@.png \n Total: %@ \n TimeStamp: %@", tracking.title, tracking.amount, tracking.note,tracking.date,tracking.pic, tracking.total, tracking.timestamp);
  
     [self.managedObjectContext save:nil];
  
     /* UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[NSString stringWithFormat:@"%@ Saved",tracking.title] message:[NSString stringWithFormat:@"Amount: %@ \n Note: %@",tracking.amount,tracking.note] delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
      [alert show];*/
  
      [amount resignFirstResponder];
      [note resignFirstResponder];
      [self dismissViewControllerAnimated:YES completion:nil];
  }
  </code></pre>