using System;

using System.Collections.Generic;

public class A

{

    public int X;

}

public class B

{

    private A a;

    public A PropA

    {

        get => this.a;

        set

        {

            if(value != null)

                this.a = value;

        }

    }

}

public class C

{

    private B b = new B()

    {

        PropA = new A()

        {

            X = 200

        }

    };

    public B PropB

    {

        get => this.b;

    }

    public C()

    {

    }

    public void DoSomeThingWithB(B b) => this.DoSomeThingWithA(b.PropA);

    public void DoSomeThingWithA(A a)

    {

        Console.WriteLine(a.X);

    }

}

public class Program

{

    public static void Print(IEnumerable<int> mt)

    {

        foreach(int x in mt)

        Console.WriteLine(x);

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var c = new C();

        Console.WriteLine(c.PropB.PropA.X);

        c.PropB.PropA.X = 5000;

        Action<B> actB = c.DoSomeThingWithB;

        actB(c.PropB);

        IList<int> intList = new List<int>(){1,2,3};

        int[] arrInt = new int[]{10,20,30};

        Print(intList);

        Print(arrInt);

    }

}