[records setValue:marbles forKey:@"marbles"];

NSNumber *marbleNumber = [NSNumber numberWithInt:marbles];
[records setObject:marbleNumber forKey@"marbles"];

[records setMarbles:[NSNumber numberWithInt:marbles]];

NSError *error;
[myManagedObjectContext save:&error];

//handle your error

+ (NSNumber *)numberWithInt:(int)value

NSNumber *myNumber = [NSNumber numberWithInt:marbles];

[records setValue:myNumber forKey:@"marbles"];

NSError *error;
        if (![context save:&error]) {
            // Update to handle the error appropriately.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            exit(-1);  // Fail
        }

NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];