C#.NET C# language. C# A modern, general-purpose object-oriented language Part of the.NET family of languages ECMA standard Based on C and C++

C#

.NET

C# language

C#

• A modern, general-purpose object-oriented language

• Part of the .NET family of languages

• ECMA standard

• Based on C and C++

.NET

• Multiple languages which can interoperate

• Languages compile to a common intermediate language

• Common Language Runtime runs programs from all the .NET languages

C# versus Java

• Both were designed to be improvements on C and C++– Java aims to be one language for many platforms

• portable (platform-independent)

• safe

– C# aims to provide many languages for a single platform• power

• unsafe code is allowed

• not platform-independent

Language Features

• Strong type checking

• Array bounds checking

• Detection of uninitialized variables

• Automatic garbage collection

• Designed for use in distributed environments

• Supports internationalization

First Programnamespace FirstProgram {

class First {

static void Main() {

System.Console.WriteLine(

"Welcome to C#!");

}

}

}

C# on onyx

• Workstations will have a Windows virtual machine with C# Express installed

C# Express

• VMWare should get installed on all the

workstations in the lab

– Not on the server

– Virtual machine is frozen

• you have to transfer any files you create onto onyx

– Use SSH Secure File Copy program

Getting your own copy

• C# Express

– Free from Microsoft

– http://www.microsoft.com/express/vcsharp/

• .NET Development Environment

– Available to you through MSDN Alliance

– details later

Keywords (reserved)

abstractas base bool break byte case

catch char checked class const continue decimal

default delegate do double else enum event

explicit extern false finally fixed float for

foreach goto if implicit in int interface

internal is lock long namespace new null

object operator out override params private protected

public readonly ref return sbyte sealed short

sizeof stackalloc static string struct switch this

throw truetry typeof uint ulong unchecked

unsafe ushort using virtual volatile void while

C# Program Structure

• A program consists of one or more files

• A file can contain one or more classes and/or namespaces– name of file is not tied to name of class

• At least one class must contain Main– There are several allowed signatures

• return type is either int or void

• either no parameter or String array

C# Types• Unified type system

– Everything can be treated as an object

• Value types– simple types: primitive types from Java plus

unsigned types and decimal

– structs

• Reference types - like object references in Java

• Pointer types - used only in unsafe code

Operators• Java operators with similar precedence

• Extra operators– typeof - returns class name (getClass())

– checked/unchecked (overflow)

– is (like instance of)

– as (returns cast value or null)

• Unsafe operators– *, &, sizeof

Operators: differences from Java

• C# allows you to overload operators

• == compares values for strings and simple types, addresses for all other objects

Console I/O

• System.Console.WriteLine( arg)– argument can be any type

– for objects, ToString is invoked

• System.Console.ReadLine()– returns a String

• System is a namespace– using System; allows you to omit the

namespace when calling the method

Namespaces

• Sort of like a package– in Java, package statement applies to everything

in the file

– can import all or part of a package

• A single C# file can contain classes from different namespaces– using imports entire namespace

C# Class Members• Function Members

– Instance constructor

– Static constructor

– Method

– Property (accessor/mutator)

– Indexer

– Operator

– Destructor (finalizer)

– Nested types (inner classes)

• Data Members– Field

• instance

• static

– Constant

– Read-only

– Delegate

– Event

C# Class Modifiers

• new

• abstract

• sealed (final)

• access modifiers– public

– protected

– internal

– private

Inheritance• Single inheritance (System.Object)

class <class_name>:<super_class> {… }

• Interfaces provide restricted form of multiple inheritanceinterface <interface_name> {… }

– Syntax for implementing is same as for inheritance

– Multiple interfaces separated by comma

– Super class, if any, must be first in list

Methods

• Same syntax as Java

• Default access is private (rather than package)

• Value types are passed by value usually– ref keyword used to pass by reference

– out keyword provides for return values

• Reference types behave as in Java

Properties

• C# properties provide the same service as Java's accessors and mutatorspublic string Color { String MyColor; get {return MyColor;} set { MyColor = value; } }

• Use the name Color to get value of or assign value to private instance variable MyColor

Object Initializerspublic class Bunny {

public string Name;

public bool LikesCarrots;

public bool LikesHumans;

public Bunny () {}

public Bunny (string n) { Name = n; }

}

Bunny b1 = new Bunny { Name="Bo", LikesCarrots=true, LikesHumans=false };

Bunny b2 = new Bunny ("Bo") { LikesCarrots=true, LikesHumans=false };

Control Statements

• do, while, for, if-else same as in Java

• foreach provides loop for arrays

• switch-case like Java except– string case values are allowed

– no fall-through behavior• use goto case <label> instead

• C# has goto statement

String

• string is alias for System.String

• reference type

– equality operators use value semantics

• Literals are written with double quotes around them

– use \ for escape character

• Verbatim string preceded by @

– escape character not supported

– can span multiple lines

string verbatim = @" verbatim string with a "" in it"

Arrays• Arrays are objects

– Subclasses of System.Array– Reverse, Sort, IndexOf methods

• Declaration, instantiation, initialization, element access as in Java for 1D arraysint []MyArray = new int[5];– Length property gives the number of elements– Only this syntax is allowed

Arrays

• For rectangular 2D arraysint [,] Array2D = new int[2,5];– Length property gives total number of

elements– Element access is the same as in Java

• For jagged arraysint [][] JaggedArray2D = new int[2][];

JaggedArray[0] = new int[3];

Structs

• A struct is very similar to a class except– structs are value types; classes are

reference types– no inheritance– struct has a default constructor always– all constructors must initialize all data– can be "instantiated” without new

Exceptions

• System.Exception

• try-catch-finally has same syntax as Java– Don't need a variable name in catch if you aren't

going to use it

– Within catch block, throw throws the exception that was caught

• All exceptions are unchecked

Delegates

• Delegate is a special type that encapsulates one or more methodspublic delegate int MyDelegate( string s, int i);

• Instantiate with a method that has the same signature and return typeMyDelegate d2 =new MyDelegate(obj.ObjectMethod);

Events

• C# event model is similar to Java - delegation based

• An Event is a special type of Delegate• Event is created by event source when an

event occurs. The Event is passed to the event consumer's handler

• Handlers must be registered with the event source

etc.

• Operator overloading• Reflection - asking a class for information

about it• Attributes

– Used to add annotation to a class that can be read using reflection

• Preprocessor• Unsafe code

mono

• mono is an open-source project that provides facilities for running C# programs under Linuxhttp://www.mono-project.com

• Compile a program by typing mcs First.cs

• Run a program by typingmono First.exe

Reference Material

• Safari books at Albertson's Library

– C# in Depth

– Learning C#

– Microsoft Visual C# Step by Step

– Programming C#