1. A Beginners Hello World public class HelloWorld { public static void Main() { System.Console.WriteLine("HELLO WORLD"); } } 2. Slightly improved version using System;

public class HelloWorld { public static void Main() { Console.WriteLine("HELLO WORLD"); } } 3. Command Line Arguments using System;

public class HelloWorld { public static void Main(string[] args) { Console.WriteLine(args[0]); } } 4. From Constructor using System; public class HelloWorld { public HelloWorld() { Console.WriteLine("HELLO WORLD"); }

public static void Main() { HelloWorld hw = new HelloWorld(); } } 5. More OO using System; public class HelloWorld { public void helloWorld() { Console.WriteLine("HELLO WORLD"); }

public static void Main() { HelloWorld hw = new HelloWorld(); hw.HelloWorld(); } } 6. From another class using System; public class HelloWorld { public static void Main() { HelloWorldHelperClass hwh = new HelloWorldHelperClass(); hwh.writeHelloWorld(); } }

public class HelloWorldHelperClass { public void writeHelloWorld() { Console.WriteLine("Hello World"); } } 7. Inheritance abstract class HelloWorldBase { public abstract void writeHelloWorld(); } class HelloWorld : HelloWorldBase { public override void writeHelloWorld() { Console.WriteLine("Hello World"); } } class HelloWorldImp { static void Main() { HelloWorldBase hwb = HelloWorld; HelloWorldBase.writeHelloWorld(); } } 8. Static Constructor using System; public class HelloWorld { private static string strHelloWorld;

static HelloWorld() { strHelloWorld = "Hello World"; } void writeHelloWorld() { Console.WriteLine(strHelloWorld); }

public static void Main() { HelloWorld hw = new HelloWorld(); hw.writeHelloWorld(); } } 9. Exception Handling using System;

public class HelloWorld { public static void Main(string[] args) { try { Console.WriteLine(args[0]); } catch(IndexOutOfRangeException e) { Console.WriteLine(e.ToString()); } } } 10. Creating a DLL and using it in an application using System;

namespace HelloLibrary { public class HelloMessage { public string Message { get { return "Hello, World!!!"; } } } }

//------

using System; using HelloLibrary;

namespace HelloApplication { class HelloApp {

public static void Main(string[] args) { HelloMessage m = new HelloMessage();

} } } 11. Using Property using System; public class HelloWorld { public string strHelloWorld { get { return "Hello World"; } }

public static void Main() { HelloWorld hw = new HelloWorld(); Console.WriteLine(cs.strHelloWorld); } } 12. Using Delegates using System; class HelloWorld { static void writeHelloWorld() { Console.WriteLine("HelloWorld"); } static void Main() { SimpleDelegate d = new SimpleDelegate(writeHelloWorld); d(); } } 13. Using Attributes #define DEBUGGING

using System; using System.Diagnostics;

public class HelloWorld : Attribute { [Conditional("DEBUGGING")]

public void writeHelloWorld() { Console.WriteLine("Hello World"); }

public static void Main() { HelloWorld hw = new HelloWorld();

hw.writeHelloWorld(); } } 14. Using Interfaces using System;

interface IHelloWorld { void writeHelloWorld(); }

public class HelloWorld : IHelloWorld { public void writeHelloWorld() { Console.WriteLine("Hello World"); }

public static void Main() { HelloWorld hw = new HelloWorld();

hw.writeHelloWorld(); } } 15. Dynamic Hello World using System; using System.Reflection;

namespace HelloWorldNS {

public class HelloWorld { public string writeHelloWorld() { return "HelloWorld"; }

public static void Main(string[] args) { Type hw = Type.GetType(args[0]);

// Instantiating a class dynamically

object[] nctorParams = new object[] {}; object nobj = Activator.CreateInstance(hw, nctorParams);

// Invoking a method

object[] nmthdParams = new object[] {}; string strHelloWorld = (string) hw.InvokeMember( "writeHelloWorld", BindingFlags.Default | BindingFlags.InvokeMethod, null, nobj, nmthdParams);

Console.WriteLine(strHelloWorld); } } } 16. Unsafe Hello World using System;

public class HelloWorld { unsafe public void writeHelloWorld(char[] chrArray) { fixed(char *parr = chrArray) { char *pch = parr; for(int i=0; i<chrArray.Length; i++) Console.Write(*(pch+i)); } }

public static void Main() { HelloWorld hw = new HelloWorld(); char[] chrHelloWorld = new char[] {'H','e','l','l','o', ' ', 'W','o','r','l','d'}; hw.writeHelloWorld(chrHelloWorld); } } 17. Using InteropServices using System; using System.Runtime.InteropServices;

class Class1 { [DllImport("kernel32")] private static extern int Beep(int dwFreq, int dwDuration);

static void Main(string[] args) { Console.WriteLine("Hello World"); Beep(1000, 2000); } }