Question

I am a beginner Objective-C programmer and I was building a calculator as my first app. I am using an NSNumberFormatter to format the Calculator’s display. It converts NSNumber to NSString correctly, but doesn’t parse NSString to NSNumber right if they have a comma separator. Here’s the code:

- (IBAction)digitPressed:(NSButton *)sender {
    if (userIsEnteringANumber) {
        NSNumber *number = [formatter numberFromString:[self.calDisplay.stringValue stringByAppendingString:sender.title]];
        self.calDisplay.stringValue = [formatter stringFromNumber:number];
    }
    else {
        self.calDisplay.stringValue = sender.title;
        userIsEnteringANumber = YES;
    }
}

If calDisplay.stringValue = @“2,569”, then pressing another digit sets number to nil.

Answer 1

Pragmatically I would simply remove the comma before parsing the string into a number then it must work.

 NSString *s = [self.calDisplay.stringValue 
                stringByReplacingOccurrencesOfString:@"," withString:@""];

Leaving you with

- (IBAction)digitPressed:(NSButton *)sender {
   if (userIsEnteringANumber) {
       NSString *s = [self.calDisplay.stringValue stringByReplacingOccurrencesOfString:@"," withString:@""];
       NSNumber *number = [formatter numberFromString:[s stringByAppendingString:sender.title]];
       self.calDisplay.stringValue = [formatter stringFromNumber:number];
   } else {
       self.calDisplay.stringValue = sender.title;
       userIsEnteringANumber = YES;
   }
}