// Hello1.cs
public class Hello1
{
   public static void Main()
   {
      System.Console.WriteLine("Hello, World!");
   }
}

Hello, World!

// Hello2.cs
using System;

public class Hello2
{
   public static void Main()
   {
      Console.WriteLine("Hello, World!");
   }
}

// Hello3.cs
// arguments: A B C D
using System;

public class Hello3
{
   public static void Main(string[] args)
   {
      Console.WriteLine("Hello, World!");
      Console.WriteLine("You entered the following {0} command line arguments:",
         args.Length );
      for (int i=0; i < args.Length; i++)
      {
         Console.WriteLine("{0}", args[i]); 
      }
   }
}

Hello, World!
You entered the following 4 command line arguments:
A
B
C
D

// Hello4.cs
using System;

public class Hello4
{
   public static int Main(string[] args)
   {
      Console.WriteLine("Hello, World!");
      return 0;
   }
}

Hello, World!

using System;

   class HelloWorld
   {
      static void Main(string[] args)
      {
         Console.WriteLine("Hello World");
         Console.ReadKey();
      }
   }