private void AddCity(string countrycode = "")
        {
            string name       = CLIHelper.GetString("Name of the city:");
            string code       = CLIHelper.GetString("Country code:");
            string district   = CLIHelper.GetString($"District {name} is in:");
            int    population = CLIHelper.GetInteger($"Population of {name}:");

            City city = new City
            {
                CountryCode = code,
                Name        = name,
                District    = district,
                Population  = population
            };

            if (String.IsNullOrEmpty(countrycode))
            {
                cityDAO.AddCity(city);
            }
            else
            {
                cityDAO.AddCityAsCapital(city, countrycode);
            }

            Console.WriteLine("City added.");
        }