Classes, properties, methods, ling begining , C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Building
    {
        public Building(){autoProp = "default";}
        public Building(string autoprop){autoProp = autoprop;}
        
        public string autoProp{get;set;}
    }
    
    public class House:Building
    {
        //properties demonstration
        bool _isBuilt;
        int _floor;
        
        //how to implement auto_property
        public string autoProp{get;set;}
        public string autoProp2{get;set;}
        
        //we can't do this in C# and .NET Framework
        //public string autoProp{get;set;} = "Default2";
        
        //this is example of private modificator in set accessor
        public int height{get;private set;}
        
        public bool isBuilt
        {
            get{return(_isBuilt);}
            set{_isBuilt = value;}
        }
        
        public int floor
        {
            get{return _floor;}
            set{
                _floor = value;
                height = value * 3;
               }
        }
        
        public House():base()
        {
            //auto property in constructor (C# versions 5 and below)
            this.autoProp = base.autoProp;//without this string autoProp = ""
            this.autoProp2 = "Default2";
        }
        public House(string s):base(s)
        {
            
        }

}
    
    public class TradeCenter:Building
    {
        int _arendators;
        public TradeCenter():base(){;}
        public TradeCenter(int arendators)
        {
            _arendators=arendators;
        }
    }
    
    //sealed means to restrict inheritance
    public sealed class BuildingsDistrict
    {
        private List<string> m_buildings = new List<string>();
        public List<string> Buildings {get{return m_buildings;}}
        //what is it?
        public BuildingsDistrict(){}
    }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            //Your code goes here
            Console.WriteLine("Hello, world!");
            
            House SmallHouse = new House();
            Console.WriteLine("isBuilt = {0}",SmallHouse.isBuilt);
            SmallHouse.isBuilt = true;
            Console.WriteLine("isBuilt = {0}",SmallHouse.isBuilt);
            
            Console.WriteLine(SmallHouse.floor);
            SmallHouse.floor = 5;
            Console.WriteLine(SmallHouse.floor);
            
            
            Console.WriteLine("House auto-prop = {0}, {1}", SmallHouse.autoProp,SmallHouse.autoProp2);
            Console.WriteLine("House Height = {0}", SmallHouse.height);
            
            
            //
            BuildingsDistrict bld = new BuildingsDistrict
            {
                Buildings={"empire","state","ostankino"}
            };

}
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,14 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,29 sec