using System;

namespace ConsoleApp1
{
    public class Program
    {
        public void Main(string[] args) {
            Person person = null;
            Console.WriteLine("house num:" + person?.Address.House);
            Console.Read();
        }
    }

    public class Person {
        public Address Address { get; set; }
    }

    public class Address {
        public int House { get; set; }
    }
}