public/internal/protected/private (พร้อมหมายเหตุเรื่อง file)

using System;

// private: only inside the class; public: everywhere the class is visible
public class Box
{
  private int _width;             // hidden storage
  public int Width                // controlled access
  {
    get { return _width; }
    set { _width = value < 0 ? 0 : value; } // simple guard
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Box b = new Box();
    // b._width = -5; // INVALID: private (kept as comment)
    b.Width = 10;      // OK: public property
    Console.WriteLine("Width = " + b.Width);
  }
}

using System;

public class BaseCounter
{
  protected int Count; // derived classes can see this
  public int Value() { return Count; }
}

public class StepCounter : BaseCounter
{
  public void Step() { Count = Count + 1; } // allowed: protected
}

public class Program
{
  public static void Main(string[] args)
  {
    StepCounter sc = new StepCounter();
    sc.Step();
    // sc.Count = 5; // INVALID from outside (commented)
    Console.WriteLine("Value = " + sc.Value());
  }
}

using System;

// internal type: visible only inside this assembly
internal class InternalHelper
{
  public static string Ping() { return "pong"; }
}

// public type can use internal from the same assembly
public class UsesInternal
{
  public string Call() { return InternalHelper.Ping(); }
}

public class Program
{
  public static void Main(string[] args)
  {
    UsesInternal u = new UsesInternal();
    Console.WriteLine(u.Call());
  }
}

using System;

public class LibraryBase
{
  // Accessible to derived types OR anywhere in the same assembly
  protected internal void Touch() { Console.WriteLine("touched"); }
}

public class LibChild : LibraryBase
{
  public void Use() { Touch(); } // via inheritance
}

public class Program
{
  public static void Main(string[] args)
  {
    LibChild c = new LibChild();
    c.Use();

    LibraryBase b = new LibraryBase();
    b.Touch(); // same assembly, allowed
  }
}