Introduction:
In this article,i am going to explain about some new features in C# 3.0.There are,

1.Implicitly typed local variables,
2.Extension Methods,
3.Anonymous types,
4.Object Intialisers,
5.Lambda Expressions,
6.Automatic Properties,

Main:

C# 3.0 provides a new keyword , var, which can be  be used in place of int, bool or string.

Implicitly typed local variables helps to infer data type as runtime,

var myInt = 0; var myBool = true; var myString = "Welcome ...";   sb.Append("myInt is a:  " + myInt.GetType().Name + "   "); sb.Append("myBool is a: " + myBool.GetType().Name + "     "); sb.Append("myString is a: " + myString.GetType().Name + "     ");   TextBox1.Text = sb.ToString();

Extension methods:

Way to extend the contract of a class by adding new  methods without creating in the
derived class or partial class.

It’s strongly typed , compiled environment such as CLR.

Extension methods can be defined for any class, including native classes of the .Net
Framework.

An extension methods is defined as a static method on a static class.

Binding between the method and type is established through the keyword ‘this’ in the
method’s prototype.

for ex,

static class myextension { public static  void DisplayType(this object obj) { Console.WriteLine(“{0} lives here ? [1] “,obj.GetType().Name,Assembly.GetAssembly(obj.GetType()))); }   int myInt = 1234; TextBox1.Text=myInt.DisplayDefiningAssembly().ToString();

Object Initializers:

C# allows to create objects directly,

Create a new object variable and assign  properties, public fields  and put object initialize
which consists of a comma-delimited list of specified values, enclosed by the { and }.

Book objbook = new Book { isbn=123;Author='James' };   List<Book> l= new List<Book> { new Person{isbn=103;Author='Peter'}, new Person{isbn=13;Author='Jenny'} ; };

Anonymous Types:

If you need a temporary type which is not intended to be reused, you can define anonymous Types.

‘var’ keyword used if user does not know at the time of writing code.

The type of the variable is inferred by compiler  (not runtime).

var mycar= new  {Color=“red”,Make=“maruthi”,Speed=“250”}; mycar.Color=“Black” ; //  but Not possible as it is readonly Console.WriteLine(“My car  color {0}”,mycar.Color) ;

Lambda Expressions:

Lambda expressions allows little coding  constructs and save lot of typing time and used in LINQ.

Lambda Expressions As a Better Anonymous Method:

List<int> evennos=list.FindAll(delegate(int ) {return I % 2}==0}}; foreach(int n in evennos) {Console.WriteLine(n);}

Automatic Properties:

Using automatic properties,we can remove set and get body properties,

for ex,
public string Name {
get
{
return name;
}
set
{ name=value; }

using automatic properties we can change the property declaration like below,

public string Name { get; set; }

public class Customer { public int CustomerId { get; private set; }   public string Name { get; set; } public string City { get; set; }   public Customer(int Id) { CustomerId = Id; }   public override string ToString() { return Name + "t" + City + "t" + CustomerId; } }   Customer c = new Customer(100); c.Name = "James"; c.City = "Dallas";

Conclusion:
Hope this helps,
Happy Coding.