c#(second day)

8/6/2019 C#(Second Day)

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C#

HCL Infosystems Ltd.


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Hierarchy

Namespace

Classes, Structure, Enumerators

Field, Methods, Indexeres, Delegates

Examples

System namesapace

Console class

Write() method


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Importing namespaces

Use the using keyword

using System;

Console.WriteLine(Hello);


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Creating Aliases

A method to define the alias or shortcut to some class or interface or

structure

Use the using keyword

using =;

e.g.

using c=System.Console;

c.WriteLine(Hello);


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Data types

Divided into two categories

Primitive or Value type

Reference Types


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Primitive or Value type

That holds values

Integrals

byte byte

short 2 byte

int 4 byte

long 8 byte

sbyte

ushort

uint

ulong

Floatings

floa

t 4 bytes 6 dec

plac

e double 8 bytes 14 dec place

decimal 16 bytes 28 dec place

Character

char 2 bytes

Booleans

bool 2 bytes


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Reference Types

string

object

Difference between in value type and reference type

Value types are stored in stack and reference in heap

Value types can never have null value assigned


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View contents of a exe file or MSIL code

Use ILDASM tool to view MSIL code

ILDASM filename.exe


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Reading Data from Keyboard

Use ReadLine() method of Console class

To convert data from String to other value types use

Parse() method of data types

We can also methods from Convert class

long Convert.ToInt64()

int Convert.ToInt32()

short Convert.ToInt16()


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Usage of @

Neutralize the meaning of escape sequence characters

Use keyword as identifier

Remove the escape sequence effect

Break stings in multi-line

string s=@ c:\amit;

Spead a string into multiple lines

string s=@ Amit

Kumar

Sharm

a;

Allow to use a keyword as indentfier

int @float;


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Conditional Statements

if

switch

ternary operator (?:)

Shortcut of if-else

Condition?true part:false part;


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Loops

while loop

do-while loop

for loop

foreach loop works with arrays and collections


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Class and Object

Aclass is a template or set of specifications to create similar set of

objects

An object is the real entity that takes some memory space for its

fields and executes its members


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Types ofmembers

Non-static or instance members always require an object to call

them

Static members or Class members Do not require any object to

call them. Accessible directly though the class name. static keyword

is required.


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Classification ofmembers

Fields to hold the value

Variable - default

Constants const keyword required and value must be

assigned while declaration

const double pi=31.4;

ReadOnly Fields Value can be assigned directly or using

constru

ctor. readonly keyword required


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Methods to do some action

Constructor

Destructor

Concrete Methods or General methods

Abstract methods

Sealed method


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Constructor

Special method which has the same name as

class

No return type

Used to initialize fields ofaclass

Can be overlo

aded

Can be private


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Destructor

Special methods which has the same name

as class name preceded by tild (~)

Calls automatically when object releases the

memory

Cannot be overloaded

By default is public, public keyword is not

allowed to use


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Abstract methods

A methods having only the signature but no body

contents

Contents are provide by overriding the methods in

child class

If declared in class, abstract keyword is required and

if declared inside an interface, no abstract keyword

required

Ifaclass contains any abstract method, it must be

declared as abstract


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Sealed method

A method that can never be overridden

sealed keyword is required


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Difference between const and readonly field

In const value must be give while declaring the

constants

const int n=5;

Readonly field can have the value while

declaration or using constructors

readonly int n;

readonly int n=5;


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Properties

Special methods that looks like fields for outside world

set and get are used to create the properties


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datatype variable;

{

set

{

Variable=value;

}

get

{

Return variable;

}

}

Objectname.propetyname=anyvalue; //set

Variable=objectname.propertyname; //get


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Types ofproperties

Read/Write properties

Having set and get

Read Only properties

Having only get

Write Only properties

Having only set


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Passing arguments to the methods

Pass by value (default)

Pass by reference (ref keyword)

When values from actual arguments get passed to formal

arguments and if we make any changes to format arguments,

they are reflected in actual arguments

Pass By output (out keyword)

To senda

variable to re

ceive the output


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Difference between ref and out

In pass by ref, variable must be initialized by in out no initialization

required


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Pillars of OOPs

Encapsulation

All members should be bundled in one body


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Abstraction orData Hiding

Provides accessibility control on the members

It is based on certain keywords

private

public

protected

internal (default)

protected internal


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Polymorphism

A method to achieve multiple activities from an item

It is achieve using the concept of overloading

Method Overloading

Operator Overloading


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Inheritance

Provides re-usability ofcode

.NET allows only single inheritance

It allows to use multiple interfaces

Use : operator to inherit aclass or interface into other

class or interface

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