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void logNumbers() {
    int start = 1, end = 10;
    for (int index = start; index <= end; index++) {
        NSLog(@"%d", index);
    }
}

void logAlphabets() {
    int start = 65, end = 90;
    for (int index = start; index <= end; index++) {
        NSLog(@"%c", index);
    }
}

-(void) viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    dispatch_queue_t aQueue;

    // Get the global concurrent queue.
    aQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_async_f(aQueue, NULL, logNumbers);
    dispatch_async_f(aQueue, NULL, logAlphabets);
}