I'm beginner on c#. I'm getting this error:

System.NullReferenceException was unhandled

and my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using GittiGidiyor;
using GittiGidiyor.City;

namespace ConsoleApplication1
    class Program
        static void Main(string[] args)
            [B]CityService cityservice = ServiceProvider.getCityService();[/B]
            cityServiceResponse response = cityservice.getCities(1, 3, "", "tr");

            if (response != null && response.ackCode.ToString().Equals("success"))
                cityType[] city = response.cities;
                foreach (cityType cities in city)

                    Console.WriteLine("citycode :" + cities.trCode + " / cityname :" + cities.cityName);
                Console.WriteLine("errorid :" + response.error.errorId);
                Console.WriteLine("errorcode :" + response.error.errorCode);
                Console.WriteLine("errormessage :" + response.error.message);

I've bolded line about getting error
I'll be glad if someone help me

Given I have no idea what GittiGidiyor is. I'll take a guess based on my own experiences. ServiceProvider.getCityService(); is not being defined/set and is not static. If it was static you could do that, if it isn't you'll have to define it as a ServiceProvider first:

ServiceProvider sProvider = new ServiceProvider();
CityService cityservice = sProvider.getCityService();

If that doesn't work. Type out (assuming you're using VC#) GittiGidiyor. and see what options it has available to use.

Yes doens't work. Thats mean not static.
I'll type gittigidiyor.
Thank you for advice