4 csharp language overview part ii 120201085223 phpapp02

8/13/2019 4 Csharp Language Overview Part II 120201085223 Phpapp02

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C# Language Overview(Part II)

Creating and Using Objects, Exceptions, Strings,Generics, Collections, Attributes

Doncho Minkov

Telerik School Academy

schoolacademy.telerik.com

Technical Trainerhttp://www.minkov.it
http://schoolacademy.telerik.com/http://minkov.it/http://minkov.it/http://schoolacademy.telerik.com/http://schoolacademy.telerik.com/


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Table of Contents

1. Creating and Using Objects

2. Exceptions Handling

3. Strings and Text Processing

4. Generics

5. Collection Classes

6. Attributes

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Using Classes and ObjectsUsing the Standard .NET Framework Classes


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What is Class?

The formal definition of class:

Definition by Google

4

Classes act as templates from which aninstance of an object is created at run

time. Classes define the properties of theobject and the methods used to controlthe object's behavior.


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Classes

Classes provide the structure for objects

Define their prototype, act as template

Classes define:

Set of attributes

Represented by fields and properties

Hold their state

Set of actions (behavior) Represented by methods

A class defines the methods and types of data

associated with an object 5


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Classes Example

6

Account

+Owner: Person+Ammount: double

+Suspend()

+Deposit(sum:double)+Withdraw(sum:double)

Class Name Attributes

(Properties

and Fields)

Operations

(Methods)


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Objects

An objectis a concrete instanceof a particularclass

Creating an object from a class is calledinstantiation

Objects have state

Set of values associated to their attributes

Example:

Class: Account

Objects: Ivan's account, Peter's account

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Objects Example

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Account

+Owner: Person+Ammount: double

+Suspend()

+Deposit(sum:double)

+Withdraw(sum:double)

Class ivanAccount+Owner="Ivan Kolev"

+Ammount=5000.0

peterAccount

+Owner="Peter Kirov"

+Ammount=1825.33

kirilAccount

+Owner="Kiril Kirov"

+Ammount=25.0

Object

Object

Object


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Classes in C#

Basic units that compose programs

Implementation is encapsulated(hidden)

Classes in C# can contain:

Fields (member variables)

Properties

Methods

Constructors

Inner types

Etc. (events, indexers, operators, ) 9


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Classes in C# Examples

Example of classes:

System.Console

System.String(stringin C#)

System.Int32(intin C#) System.Array

System.Math

System.Random

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Declaring Objects

An instance of a class or structure can bedefined like any other variable:

Instances cannot be used if they are

not initialized

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using System;

...

// Define two variables of type DateTimeDateTime today;

DateTime halloween;

// Declare and initialize a structure instanceDateTime today = DateTime.Now;


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Fields

Fields are data members of a class

Can be variables and constants

Accessing a field doesnt invoke any actions of

the object Example:

String.Empty(the ""string)

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Accessing Fields

Constant fields can be only read

Variable fields can be read and modified

Usually properties are used instead of directly

accessing variable fields Examples:

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// Accessing read-only field

String empty = String.Empty;

// Accessing constant fieldint maxInt = Int32.MaxValue;


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Properties

Properties look like fields (have name and

type), but they can contain code, executedwhen they are accessed

Usually used to control access to data

fields (wrappers), but can contain morecomplex logic

Can have two components (and at least oneof them) called accessors

getfor reading their value

setfor changing their value14


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Properties (2)

According to the implemented accessorsproperties can be:

Read-only (getaccessor only)

Read and write (both getand setaccessors) Write-only (setaccessor only)

Example of read-only property:

String.Length

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Accessing Properties and Fields Example

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using System;...DateTime christmas = new DateTime(2009, 12, 25);int day = christmas.Day;int month = christmas.Month;

int year = christmas.Year;

Console.WriteLine("Christmas day: {0}, month: {1}, year: {2}",day, month, year);

Console.WriteLine("Day of year: {0}", christmas.DayOfYear);

Console.WriteLine("Is {0} leap year: {1}",year, DateTime.IsLeapYear(year));


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Instance and Static Members

Fields, properties and methods can be:

Instance(or object members)

Static(or class members)

Instancemembersare specific for each object Example: different dogs have different name

Staticmembersare common for all instances

of a class

Example: DateTime.MinValueis sharedbetween all instances of DateTime

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Instance and StaticMembers Examples

Example of instance member String.Length

Each string object has different length

Example of static member

Console.ReadLine()

The console is only one (global for the program)

Reading from the console does not require tocreate an instance of it

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Methods

Methods manipulate the data of the object towhich they belong or perform other tasks

Examples:

Console.WriteLine() Console.ReadLine()

String.Substring(index, length)

Array.GetLength(index)

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Instance Methods

Instance methods manipulate the data of aspecified object or perform any other tasks

If a value is returned, it depends on theparticular class instance

Syntax:

The name of the instance, followed by the

name of the method, separated by dot

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.()


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Calling Instance Methods Examples

Calling instance methods of String:

Calling instance methods of DateTime:

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String sampleLower = new String('a', 5);String sampleUpper = sampleLower.ToUpper();

Console.WriteLine(sampleLower); // aaaaa

Console.WriteLine(sampleUpper); // AAAAA

DateTime now = DateTime.Now;DateTime later = now.AddHours(8);

Console.WriteLine("Now: {0}", now);Console.WriteLine("8 hours later: {0}", later);


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Static Methods

Static methods are common for all instances ofa class (shared between all instances)

Returned value depends only on the passedparameters

No particular class instance is available

Syntax:

The name of the class, followed by the name ofthe method, separated by dot

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.()


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Calling Static Methods Examples

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using System;

double radius = 2.9;double area = Math.PI * Math.Pow(radius, 2);Console.WriteLine("Area: {0}", area);

// Area: 26,4207942166902

double precise = 8.7654321;double round3 = Math.Round(precise, 3);double round1 = Math.Round(precise, 1);Console.WriteLine(

"{0}; {1}; {2}", precise, round3, round1);// 8,7654321; 8,765; 8,8

Constantfield Staticmethod

Staticmethod

Staticmethod


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Constructors

Constructors are special methods used toassign initial values of the fields in an object

Executed when an object of a given type isbeing created

Have the same name as the class that holdsthem

Do not return a value

A class may have several constructors withdifferent set of parameters

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Constructors (2)

Constructor is invoked by the newoperator

Examples:

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String s = new String("Hello!"); // s = "Hello!"

= new ()

String s = new String('*', 5); // s = "*****"

DateTime dt = new DateTime(2009, 12, 30);

DateTime dt = new DateTime(2009, 12, 30, 12, 33, 59);

Int32 value = new Int32(1024);


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Structures

Structures are similar to classes

Structures are usually used for storing datastructures, without any other functionality

Structures can have fields, properties, etc. Using methods is not recommended

Structures are value types, and classes are

reference types(this will be discussed later) Example of structure

System.DateTimerepresents a date and time26


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What is a Namespace?

Namespaces are used to organize the source

code into more logical and manageable way

Namespaces can contain

Definitions of classes, structures, interfaces andother types and other namespaces

Namespaces can contain other namespaces

For example: Systemnamespace contains Datanamespace

The name of the nested namespace is

System.Data 27


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Full Class Names

A full name of a class is the name of the classpreceded by the name of its namespace

Example: Arrayclass, defined in the Systemnamespace

The full name of the class is System.Array

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.


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Including Namespaces

The usingdirective in C#:

Allows using types in a namespace, without

specifying their full nameExample:

instead of

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using

using System;

DateTime date;

System.DateTime date;


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Common Type System (CTS)

CTS defines all data typessupported in .NETFramework

Primitive types (e.g. int, float, object)

Classes (e.g. String, Console, Array)

Structures (e.g. DateTime)

Arrays (e.g. int[], string[,])

Etc.

Object-oriented by design

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CTS and Different Languages

CTS is common for all .NET languages

C#, VB.NET, J#, JScript.NET, ...

CTS type mappings:

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CTS Type C# Type VB.NET Type

System.Int32 int Integer

System.Single float Single

System.Boolean bool Boolean

System.String string String

System.Object object Object


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Value and Reference Types

In CTS there are two categories of types

Valuetypes Reference types

Placed in different areas of memory Value types live in the execution stack

Freed when become out of scope

Reference types live in the managed heap(dynamic memory)

Freed by the garbage collector

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Value and Reference Types


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Value and Reference Types Examples

Value types

Most of the primitive types

Structures

Examples: int, float, bool, DateTime Reference types

Classes and interfaces

Strings

Arrays

Examples: string, Random, object, int[] 33


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Exceptions HandlingThe Paradigm of Exceptions in OOP


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What are Exceptions?

The exceptions in .NET Framework are classicimplementation of the OOP exception model

Deliver powerful mechanism for centralizedhandling of errors and unusual events

Substitute procedure-oriented approach,in which each function returns error code

Simplify code construction and maintenance Allow the problematic situations to be

processed at multiple levels

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Handling Exceptions

In C# the exceptions can be handled by the

try-catch-finallyconstruction

catchblocks can be used multiple times toprocess different exception types

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try{

// Do some work that can raise an exception}catch (SomeException){

// Handle the caught exception}


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Handling Exceptions Example

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static void Main(){

string s = Console.ReadLine();try{

Int32.Parse(s);Console.WriteLine(

"You entered valid Int32 number {0}.", s);}catch(FormatException){

Console.WriteLine("Invalid integer number!");}

catch(OverflowException){

Console.WriteLine("The number is too big to fit in Int32!");

}}

h i l


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The System.ExceptionClass

Exceptions in .NET are objects

The System.Exceptionclass is base for allexceptions in CLR

Contains information for the cause of the erroror the unusual situation

Messagetext description of the exception

StackTracethe snapshot of the stack at themoment of exception throwing

InnerExceptionexception caused the currentexception (if any)

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Exception Properties Example

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class ExceptionsTest

{ public static void CauseFormatException(){

string s = "an invalid number";Int32.Parse(s);

}static void Main(){

try{

CauseFormatException();}catch (FormatException fe)

{Console.Error.WriteLine("Exception caught:{0}\n{1}", fe.Message, fe.StackTrace);

}}

}


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E i P i ( )


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Exception Properties (2)

File names and line numbers are accessible only if the

compilation was in Debugmode

When compiled in Releasemode, the information inthe property StackTraceis quite different:

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Exception caught: Input string was not in a correctformat.

at System.Number.ParseInt32(String s, NumberStylesstyle, NumberFormatInfo info)

at ExceptionsTest.Main(String[] args)

E i Hi h


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Exception Hierarchy

Exceptions in .NET Framework are organizedin a hierarchy

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T f E i


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Types of Exceptions

All .NET exceptions inherit from System.Exception

The system exceptions inherit from

System.SystemException, e.g.

System.ArgumentException

System.NullReferenceException

System.OutOfMemoryException

System.StackOverflowException

User-defined exceptions should inherit fromSystem.ApplicationException

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H dli E ti


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Handling Exceptions

When catching an exception of a particular class, all

its inheritors (child exceptions) are caught too

Example:

Handles ArithmeticExceptionand its successorsDivideByZeroExceptionand OverflowException

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try{

// Do some works that can raise an exception}catch (System.ArithmeticException){

// Handle the caught arithmetic exception}

H dli All E ti


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Handling All Exceptions

All exceptions thrown by .NET managed codeinherit the System.Exceptionexception

Unmanaged code can throw other exceptions

For handling all exceptions (even unmanaged)use the construction:

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try{

// Do some works that can raise any exception

}catch{

// Handle the caught exception}


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H E ti W k?


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How Exceptions Work?

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Main()

Method 1

Method 2

Method N

2. Method call

3. Method call

4. Method call

Main()

Method 1

Method 2

Method N

8. Find handler

7. Find handler

6. Find handler

5. Throw an exception

.NETCLR


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Th i E ti E l


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Throwing Exceptions Example

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public static double Sqrt(double value){

if (value < 0)throw new System.ArgumentOutOfRangeException(

"Sqrt for negative numbers is undefined!");return Math.Sqrt(value);

}static void Main(){

try{

Sqrt(-1);}

catch (ArgumentOutOfRangeException ex){Console.Error.WriteLine("Error: " + ex.Message);throw;

}}


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Strings and Text Processing

What Is String?


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What Is String?

Strings are sequences of characters

Each character is a Unicode symbol

Represented by the stringdata type in C#

(System.String) Example:

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string s = "Hello, C#";

H e l l o , C #s

The System StringClass


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The System.StringClass

Strings are represented by System.Stringobjects in .NET Framework

String objects contain an immutable (read-only)sequence of characters

Strings use Unicode in to support multiplelanguages and alphabets

Strings are stored in the dynamic memory(managed heap)

System.Stringis reference type

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The System String Class (2)


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The System.StringClass (2)

String objects are like arrays of characters

(char[])

Have fixed length (String.Length)

Elements can be accessed directly by index

The index is in the range [0...Length-1]

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string s = "Hello!";int len = s.Length; // len = 6char ch = s[1]; // ch = 'e'

0 1 2 3 4 5

H e l l o !

index =s[index] =

Strings Example


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Strings Example

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static void Main(){

string s =

"Stand up, stand up, Balkan Superman.";

Console.WriteLine("s = \"{0}\"", s);

Console.WriteLine("s.Length = {0}", s.Length);

for (int i = 0; i < s.Length; i++)

{

Console.WriteLine("s[{0}] = {1}", i, s[i]);

}}

Declaring Strings


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Declaring Strings

There are two ways of declaring string

variables:

Using the C# keyword string

Using the .NET's fully qualified class nameSystem.String

The above three declarations are equivalent

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string str1;

System.String str2;

String str3;

Creating Strings


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Creating Strings

Before initializing a string variable has null

value

Strings can be initialized by:

Assigning a string literal to the string variable Assigning the value of another string variable

Assigning the result of operation of type string

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Creating Strings (2)


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Creating Strings (2)

Not initialized variables has value of null

Assigning a string literal

Assigning from another string variable

Assigning from the result of string operation

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string s; // s is equal to null

string s = "I am a string literal!";

string s2 = s;

string s = 42.ToString();

Reading and Printing Strings


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Reading and Printing Strings

Reading strings from the console Use the method Console.ReadLine()

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string s = Console.ReadLine();

Console.Write("Please enter your name: ");string name = Console.ReadLine();

Console.Write("Hello, {0}! ", name);

Console.WriteLine("Welcome to our party!");

Printing strings to the console

Use the methods Write() and WriteLine()

Comparing Strings


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Comparing Strings

A number of ways exist to compare two

strings:

Dictionary-based string comparison

Case-insensitive

Case-sensitive

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int result = string.Compare(str1, str2, true);// result == 0 if str1 equals str2// result < 0 if str1 if before str2// result > 0 if str1 if after str2

string.Compare(str1, str2, false);

Comparing Strings Example


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Comparing Strings Example

Finding the first string in a lexicographical order

from a given list of strings:

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string[] towns = {"Sofia", "Varna", "Plovdiv","Pleven", "Bourgas", "Rousse", "Yambol"};

string firstTown = towns[0];for (int i=1; i


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Concatenating Strings

There are two ways to combine strings:

Using the Concat()method

Using the +or the +=operators

Any object can be appended to string

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string str = String.Concat(str1, str2);

string str = str1 + str2 + str3;string str += str1;

string name = "Peter";int age = 22;string s = name + " " + age; // "Peter 22"

Searching in Strings


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Searching in Strings

Finding a character or substring within givenstring

First occurrence

First occurrence starting at given position

Last occurrence

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IndexOf(string str)

IndexOf(string str, int startIndex)

LastIndexOf(string)

Searching in Strings Example


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Searching in Strings Example

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string str = "C# Programming Course";int index = str.IndexOf("C#"); // index = 0index = str.IndexOf("Course"); // index = 15index = str.IndexOf("COURSE"); // index = -1// IndexOf is case-sensetive. -1 means not foundindex = str.IndexOf("ram"); // index = 7index = str.IndexOf("r"); // index = 4index = str.IndexOf("r", 5); // index = 7index = str.IndexOf("r", 8); // index = 18

0 1 2 3 4 5 6 7 8 9 10 11 12 13

C # P r o g r a m m i n g

index =

s[index] =

Extracting Substrings


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Extracting Substrings

Extracting substrings

str.Substring(int startIndex, int length)

str.Substring(int startIndex)

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string filename = @"C:\Pics\Rila2009.jpg";string name = filename.Substring(8, 8);// name is Rila2009

string filename = @"C:\Pics\Summer2009.jpg";string nameAndExtension = filename.Substring(8);

// nameAndExtension is Summer2009.jpg

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

C : \ P i c s \ R i l a 2 0 0 5 . j p g

Splitting Strings


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Splitting Strings

To split a string by given separator(s) use the

following method:

Example:

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string[] Split(params char[])

string listOfBeers ="Amstel, Zagorka, Tuborg, Becks.";string[] beers =listOfBeers.Split(' ', ',', '.');

Console.WriteLine("Available beers are:");foreach (string beer in beers){

Console.WriteLine(beer);}

Replacing and Deleting Substrings


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Replacing and Deleting Substrings

Replace(string,string)replaces all

occurrences of given string with another

The result is new string (strings are immutable)

Remove(index,length)deletes part of a string

and produces new string as result

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string cocktail = "Vodka + Martini + Cherry";string replaced = cocktail.Replace("+", "and");

// Vodka and Martini and Cherry

string price = "$ 1234567";string lowPrice = price.Remove(2, 3);// $ 4567

Changing Character Casing


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Changing Character Casing

Using method ToLower()

Using method ToUpper()

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string alpha = "aBcDeFg";string lowerAlpha = alpha.ToLower(); // abcdefgConsole.WriteLine(lowerAlpha);

string alpha = "aBcDeFg";string upperAlpha = alpha.ToUpper(); // ABCDEFGConsole.WriteLine(upperAlpha);

Trimming White Space


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Trimming White Space

Using method Trim()

Using method Trim(chars)

Using TrimStart()and TrimEnd()

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string s = " example of white space ";string clean = s.Trim();Console.WriteLine(clean);

string s = " \t\nHello!!! \n";string clean = s.Trim(' ', ',' ,'!', '\n','\t');Console.WriteLine(clean); // Hello

string s = " C# ";string clean = s.TrimStart(); // clean = "C# "

Constructing Strings


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Constructing Strings

Strings are immutable

Concat(), Replace(), Trim(), ... return newstring, do not modify the old one

Do not use "+" for strings in a loop!

It runs very, very inefficiently!

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public static string DupChar(char ch, int count){

string result = "";for (int i=0; i


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g g gStringBuilder

Use the System.Text.StringBuilderclass formodifiable strings of characters:

Use StringBuilderif you need to keep addingcharacters to a string

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public static string ReverseString(string s){

StringBuilder sb = new StringBuilder();for (int i = s.Length-1; i >= 0; i--)

sb.Append(s[i]);return sb.ToString();

}

The StringBuilder Class


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The StringBuilder Class

StringBuilderkeeps a buffer memory,

allocated in advance Most operations use the buffer memory and

do not allocate new objects

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H e l l o , C # !StringBuilder:

Length=9

Capacity=15

Capacity

used buffer

(Length)

unusedbuffer

StringBuilder Example


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StringBuilder Example

Extracting all capital letters from a string

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public static string ExtractCapitals(string s){

StringBuilder result = new StringBuilder();for (int i = 0; i


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Method ToString()

All classes have public virtual method

ToString()

Returns a human-readable, culture-sensitivestring representing the object

Most .NET Framework types have ownimplementation of ToString()

int, float, bool, DateTime

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int number = 5;string s = "The number is " + number.ToString();Console.WriteLine(s); // The number is 5

Method ToString(format)


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Method ToString(format)

We can apply specific formatting when

converting objects to string

ToString(formatString)method

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int number = 42;string s = number.ToString("D5"); // 00042

s = number.ToString("X"); // 2A

// Consider the default culture is Bulgarians = number.ToString("C"); // 42,00

double d = 0.375;s = d.ToString("P2"); // 37,50 %

Formatting Strings


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Formatting Strings

The formatting strings are different for the

different types

Some formatting strings for numbers:

Dnumber (for integer types)

Ccurrency (according to current culture)

Enumber in exponential notation

Ppercentage

Xhexadecimal number

Ffixed point (for real numbers)

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Method String.Format()


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Method String.Format()

Applies templatesfor formatting strings

Placeholders are used for dynamic text

Like Console.WriteLine()

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string template = "If I were {0}, I would {1}.";string sentence1 = String.Format(template, "developer", "know C#");

Console.WriteLine(sentence1);// If I were developer, I would know C#.

string sentence2 = String.Format(template, "elephant", "weigh 4500 kg");

Console.WriteLine(sentence2);// If I were elephant, I would weigh 4500 kg.

Composite Formatting


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Composite Formatting

The placeholders in the composite formatting

strings are specified as follows:

Examples:

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{index[,alignment][:formatString]}

double d = 0.375;s = String.Format("{0,10:F5}", d);// s = " 0,37500"

int number = 42;Console.WriteLine("Dec {0:D} = Hex {1:X}",

number, number);// Dec 42 = Hex 2A

Formatting Dates


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Formatting Dates

Dates have their own formatting strings

d, ddday (with/without leading zero)

M, MMmonth

yy, yyyyyear (2 or 4 digits) h, HH, m, mm, s, sshour, minute, second

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DateTime now = DateTime.Now;

Console.WriteLine("Now is {0:d.MM.yyyy HH:mm:ss}", now);

// Now is 31.11.2009 11:30:32


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Collection Classes

Lists, Trees, Dictionaries

What are Generics?


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Generics allow defining parameterized classes

that process data of unknown (generic) type The class can be instantiated with several

different particular types

Example: List List/List/ List

Generics are also known as "parameterized

types" or "template types"

Similar to the templates in C++

Similar to the generics in Java80

The ListClass


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Implements the abstract data structure list

using an array

All elements are of the same type T

Tcan be any type, e.g. List,List, List

Size is dynamically increased as needed

Basic functionality: Countreturns the number of elements

Add(T)appends given element at the end

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ListSimple Example


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p p

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static void Main()

{ List list = new List();

list.Add("C#");list.Add("Java");list.Add("PHP");

foreach (string item in list){

Console.WriteLine(item);}

// Result:// C#// Java// PHP

}

ListFunctionality


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y

list[index]access element by index

Insert(index,T)inserts given element to thelist at a specified position

Remove(T)removes the first occurrence of

given element

RemoveAt(index)removes the element at thespecified position

Clear()removes all elements

Contains(T)determines whether an elementis part of the list

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ListFunctionality (2)


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y ( )

IndexOf()returns the index of the first

occurrence of a value in the list (zero-based)

Reverse()reverses the order of the elements inthe list or a portion of it

Sort()sorts the elements in the list or aportion of it

ToArray()converts the elements of the list to

an array

TrimExcess()sets the capacity to the actualnumber of elements

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Primes in an Interval Example


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p

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static List FindPrimes(int start, int end){

List primesList = new List();

for (int num = start; num


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Implements the stackdata structure using an

array

Elements are of the same type T

Tcan be any type, e.g. Stack


Basic functionality:

Push(T)inserts elements to the stack Pop()removes and returns the top element

from the stack

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StackExample


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p

Using Push(), Pop()and Peek()methods

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static void Main(){

Stack stack = new Stack();

stack.Push("1. Ivan");

stack.Push("2. Nikolay");stack.Push("3. Maria");stack.Push("4. George");

Console.WriteLine("Top = {0}", stack.Peek());

while (stack.Count > 0)

{ string personName = stack.Pop();Console.WriteLine(personName);

}}

The QueueClass


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Q

Implements the queue data structure using a

circular resizable array Elements are from the same type T

Tcan be any type, e.g. Stack


Basic functionality:

Enqueue(T)adds an element to theend of the queue

Dequeue()removes and returns theelement at the beginning of the queue

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QueueExample


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Q p

Using Enqueue()and Dequeue()methods

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static void Main(){

Queue queue = new Queue();

queue.Enqueue("Message One");

queue.Enqueue("Message Two");queue.Enqueue("Message Three");queue.Enqueue("Message Four");

while (queue.Count > 0){

string message = queue.Dequeue();Console.WriteLine(message);

}}

DictionaryClass


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y y

Implements the abstract data type

"Dictionary" as hash table


Contains a collection of key-and-valuepairs arranged by the hash code of thekey h(key) = value

Collisions are resolved by chaining

Dictionaryclass relies on

Object.Equals()method forcomparing elements

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DictionaryClass(2)


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(2) Object.GetHashCode()method for

calculating the hash codes of the elements Major operations:

Add(TKey,TValue)adds an element

with the specified key and value into thedictionary

Remove(TKey)removes the element with

the specified key Clear()removes all elements

this[]returns element by key91

DictionaryClass(3)


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(3) Countreturns the number of elements

ContainsKey(TKey)determines whetherthe dictionary contains given key

ContainsValue(TValue)determines

whether the dictionary contains given value

Keysreturns a collection of the keys

Valuesreturns a collection of the values

TryGetValue(TKey,out TValue)if the keyis found, returns it in the TValue, otherwisereturns the default value for the TValuetype

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DictionaryExample


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Example

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Dictionary studentsMarks= new Dictionary();

studentsMarks.Add("Ivan", 4);studentsMarks.Add("Peter", 6);studentsMarks.Add("Maria", 6);studentsMarks.Add("George", 5);int peterMark = studentsMarks["Peter"];

Console.WriteLine("Peter's mark: {0}", peterMark);Console.WriteLine("Is Peter in the hash table: {0}",

studentsMarks.ContainsKey("Peter"));Console.WriteLine("Students and grades:");

foreach (var pair in studentsMarks){Console.WriteLine("{0} --> {1} ", pair.Key,

pair.Value);}

Counting Words in Given Text


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string text = "Welcome to our C# course. In this " +"course you will learn how to write simple " +

"programs in C# and Microsoft .NET";string[] words = text.Split(new char[] {' ', ',', '.'},StringSplitOptions.RemoveEmptyEntries);var wordsCount = new Dictionary();

foreach (string word in words)

{if (wordsCount.ContainsKey(word))wordsCount[word]++;elsewordsCount.Add(word, 1);

}

foreach (var pair in wordsCount){Console.WriteLine("{0} --> {1}", pair.Key, pair.Value);

}

Balanced Trees in .NET


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Balanced Binary Search Trees

Ordered binary search trees that have height oflog2(n)where nis the number of their nodes

Searching costs about log2(n)comparisons

.NET Framework has built-in implementationsof balanced search trees, e.g.:

SortedDictionary

Red-black tree based map of key-value pairs

External libraries like "Wintellect PowerCollections for .NET" are more flexible

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Sorted Dictionary Example


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string text = "Welcome to our C# course. In this " +"course you will learn how to write simple " +

"programs in C# and Microsoft .NET";string[] words = text.Split(new char[] {' ', ',', '.'},StringSplitOptions.RemoveEmptyEntries);var wordsCount = new SortedDictionary();

foreach (string word in words){

if (wordsCount.ContainsKey(word))wordsCount[word]++;elsewordsCount.Add(word, 1);

}

foreach (var pair in wordsCount){Console.WriteLine("{0} --> {1}", pair.Key, pair.Value);

}


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AttributesWhat They Are? How and When to Use Them?

What Are Attributes?


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Special declarative tags for attaching

descriptive information (annotations) to thedeclarations in the code

At compile time attributes are saved in the

assembly's metadata

Can be extracted from the metadata and canbe manipulated by different tools

Instances of classes derived fromSystem.Attribute

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Attributes Applying Example


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Attribute's name is surrounded by square

brackets and is placed before the declarationwhich it refers to:

[Flags]attribute indicates that the enumtype can be treated like a set of bit flags

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[Flags] // System.FlagsAttribute

public enum FileAccess{Read = 1,Write = 2,ReadWrite = Read | Write

}

Attributes With Parameters


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Attributes use parameters for initialization:

In the example the [DllImport]attribute isinstantiated by the compiler as follows:

An object of System.Runtime.InteropServices.DllImportAttributeclass is created and initialized

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[DllImport("user32.dll", EntryPoint="MessageBox")]public static extern int ShowMessageBox(int hWnd,string text, string caption, int type);...ShowMessageBox(0, "Some text", "Some caption", 0);

C# Language Overview(Part II)


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(Part II)

Questions?

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