chuong 2 basic c#

8/3/2019 Chuong 2 Basic C#

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Chng 2 C# Language Fundamentals


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N i dung C ch vi t 1 console application

Console I/ 0 v lnh nh p xu t Khai b o bi n:

Strongly type Implicited type local variable

C c ki u d li u Value type Reference type

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N i dung (tt) Chuy n i ki u Boxing and unboxing Tham s ref, out, param

L nh lp for, while, do while, foreach L nh ph n nh nh switch, l nh nhy C c ki u d li u ph c:

Enumeration Struct Array

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Visual studio 2008 environment

L mt mi tr ng l p tr nh nhi u cng c(tool-rich programming environment) ch a m i

nh nng c n thi t t o c c d n C# t nh n l n

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Basic C# syntax

C# code is made up of a series of statements,each of which is terminated with a semicolon.

C# is a block-structured language {} C# code is that it is case sensitive.

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Console Application

Console Application : l ng d ng m input voutput u n m trong console window.

Console window: c n g i l c a s d u nh cl nh (MS-DOS command prompt)

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ng d ng console C# u tin

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// Ch ng trnh C# u tin

using System;using System.Collections.Generic;using System.Text;

namespace HelloWorld {

class Program {

static void Main( string [] args)

{ Console .Write( "Hello World!" );Console .ReadLine();

}}

}


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Cu trc chng tr nh C# Ph n ch thch (option)

Ph n khai b o dng namespace (option)

Ph n nh ngha namespace v l p

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// Ch ng trnh C# u tin

using System;using System.Collections.Generic;using System.Text;


class Program {static void Main( string [] args){ {Console .Write( "Hello World!" );Console .ReadLine();

}}

}


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C u l nh (Statement) C c c u l nh c vi t trong th n ca phnth c (method) Th c hi n m t cng vi c n o

K t thc bi du chm phy (; )

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class Program {

static void Main( string [] args){

Console .Write( "Hello World!" );Console .ReadLine();

}}

}

Cc cu lnh

Phng thc Main


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Khong tr ng

Bao gm K t tr ng, k t xung d ng, k t tab D ng trng

S d ng hp l chng tr nh d c

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namespace HelloWorld { class Program

{

static void Main( string [] args){Console .Write( "Hello World!" );

Console .ReadLine();}}}


class Program {

static void Main( string [] args){

Console .Write( "Hello World!" );Console .ReadLine();

}}

}


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Ch thch

Ch thch (comment) c dng gii thchv chng tr nh v c c c u l nh

Gip cho chng tr nh d hi u hn c b qua khi bin dch Khng nh hng t i k t qu th c thi ca

chng tr nh C th ph t sinh ra documentation ca chng

trnh qua ch thch XML

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Hai c ch t o ch thch c bn

G ph n ch thch sau cp k t// G ph n ch thch gi a cp k t/* v */

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/* Ch ng trnh C# u tin In ra cu cho "Hello World" */

using System;


class Program {

static void Main(string[] args){

Console.Write("Hello World!"); // Xut ra cu cho Console.ReadLine(); // Ch nhn Enter

}}

}


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XML Comment

Cho php ph t sinh ra su li u d ng XML Thch hp cho vi c vi t su li u ca d n l

Ch thch XML b t u v i triple slash (///)v c c tag ca XML Ch thch XML dng cho

User defined types Class, delegate, enum and struct Member of user defined types

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V d : ng d ng CONSOLE n gin

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Using Namespace

gii quy t v n xung t tn (name-crashing) nn t o 1 container c t tn

namespace Hai class c th trng tn nhau nhng khng bi s

d ng nh m l n n u thu c 2 namespace kh c nhau

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Tn y TextHello.Greeting


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Using Namespace

C c class trong .NET framework c ng c s px p v o c c namespace kh c nhau.

V d : l p Console thu c namespace System tham chi u n 1 l p n o , c th dng

tn y :Namespace.ClassName

Hoc tr nh phi vi t y tham chi u nnamespace, c th dng using directive uchng trnh

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Using Namespace

Bn namespace thng d ng hay c dngtrong c c chng trnh s c Visual Studiot ng a vo u m i chng trnh m i.

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File program.cs

M t chng tr nh n gin nh t bao gm: 1file program.cs, trong file c 1 namespace mcnh v 1 class.

Class: phi c ti thi u1 hm Main

static void Main( string[] args)

{}

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Tnh nng IntelliSense ca IDE

T ng hi n th danh s ch c c th nh ph nca class khi l nh c g v o c a s so ntho.

C# s hi n th th nh ph n (member) ph hpv i c c k t ang c g v o, sau hi nth tool tip ch a m t nh nng ca th nhph n.

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Console I/O

c k t vn bn t c a s console Console.Read() gi tr tr v l int

Console.ReadLine() gi tr tr v l string

xut chu i k t dng Console.Write() / Console.WriteLine()

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Printing on the Console

nh d ng vn bn xu t ra:Console.WriteLine( "{0}\n{1}",

"Welcome to", "C# Programming!" );

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i s cha chu i nh dang

i s 0 i s 1


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K t nh d ng chu i

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Console I/O

Console.WriteLine()

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\ n: k t xung dng


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Console I/O

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/ F5

Xut chui c chui

Ch c 1 dng, mc ch l dng mn hnh


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C# Is a strongly Typed Language

C# l mt ngn ng c kim sot chtch v mt kiu d liu

M i bi n (variable) v i tng (objectinstance) trong h thng phi c x c nhki u t ng minh (well-defined type)

Cho php compiler d d ng ki m tra c nh hp l c c php to n trn c c bi n v i

tng.

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Khai b o bi n

Khai b o bi n theo 2 d ng: ; =; Hay dng k t hp c 2 d ng

V d : int xSize, ySize; int age = 25; int xSize, ySize = 5;

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Variable name

Hai quy t c: K t u phi l ch ci (letter) hoc d u _ hoc

@. C c k t p theo c th l ch ci, _ hay s.

Ph n bi t CH HOA v ch th ng Phi kh c v i t kha (dng @ kh c ph c)

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G n gi tr bi n

Assign operator: = Ex

myInteger = 17;myString = "\"myInteger\" is";

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Ph m vi bi n

Ph m vi (scope) c x c nh bi cp du{ v } C th ch a ph m vi nh hn

V tr khai b o bi n Trong th n phng th c: bi n c c b Trong th n l p(trong class): thu c tnh

Bi n trong C# ch c t c d ng trong ph m vim n c khai b o

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Keyword

abstract const extern in operator sbyte throw viras continue false int out sealed true voidbase decimal finally interface override set try vobool default fixed internal params short typeof wbreak delegate float is partial sizeof uint whbyte do for lock private stackalloc ulong yiecase double foreach long protected static uncheckedcatch else get namespace public string unsafe

char enum goto new readonly struct ushortchecked event if null ref switch usingclass explicit implicit object return this value

Cc t kha trong C# 2005

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Data types

There are two kinds of data types in C#. Value Types (implicit data types, structs and

enumeration)

Reference Types (objects, delegates)

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Values types

Bi n lo i tham tr (value types) ch a 1 gi trc th ca lo i d li u n o .

V d : bi n snguyn (int) ch a gi tr7

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Reference types

Bi n lo i tham chi u ch a a ch b nh ch ad li u m bi n tham chi u n.

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Reference type

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String s1= "Hello";

"Hello"

"Bye"s2

s3

s1

string s2 = "Bye";string s3;s3 = s1;


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Implicit data types

M i ki u d li u ng m nh u c nh xth nh m t ki u tng ng trong CommonType System (CTS) v CLS (Common LanguageSpecification).

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C c ki u d li u ng m nh trong C#

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C c ki u d li u ng m nh trong C#

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B nh my nh c t ch c nh th no?

H iu h nh chia b nh th nh 2 chunk kh cnhau, m i chunk c qun ltheo 1 c chkh c nhau.

Stack Heap

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Value types v reference types

T t c lo i tham tr (value) u c t o trnstack.

T t c lo i tham bi n (reference) u c t otrn heap Nhng con tr tham chi u (reference pointer) th

n m trn stack.

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Stack

A stack is a data structure that store items ina first in first out (FIFO) fashion. It is an area of memory supported by the processor and its

size is determined at the compile time.

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Heap

A heap consists of memory available to theprogram at run time. Reference types areallocated using memory available from theheap dynamically (during the execution of program). The garbage collector searches fornon-referenced data in heap during theexecution of program and returns that space

to Operating System.

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Value type vs. Reference type

Characteristic Value type Reference type

Variable hold Value ReferenceAllocated Stack Heap

Default Zero Null

Parameter Copy value Copy reference

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Constant

M t h ng l m t bi n nhng tr khng thay const int a = 100 ; // gi tr ko th thay i

H ng b t bu c phi c g n gi tr lc khaibo

Tr ca h ng c th c tnh to n v o lc bi

dch H ng bao gi c ng static

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Constant

u i m Chng tr nh d c, kh c ph c nh ng con s

magic number trong code. Chng tr nh d s a hn. Tr nh l i d d ng hn, tr nh bin dch s b o l i

n u g n l i gi tr cho h ng

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Minh h a s d ng h ng

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nh ngha hng

Constant


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readonly

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const : phi c gn gi tr khi khai boreadonly : ko cn khi to trc , khi gn gi tr th sau ko thayi c

Cha c khi gn

Ko c thay i


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Implicitly Typed Local Variables

In C#, every variable declared in the codemust have an explicit type associated with it.But sometimes, when writing code for strongly

typed languages, the amount of typingneeded to declare such variables can betedious

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Bi lo i di


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Bi n lo i suy dinType inference

var l t kha m i trong C# 3.0 C ch khai b o:

var =;

Bi n c lo i ng m nh l lo i cavalue.

V d : var myVar = 5;myVar l bi n lo i int

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using System;using System.Collections.Generic;

public class EntryPoint{static void Main(){

var myList = new List();myList.Add( 1 );myList.Add( 2 );myList.Add( 3 );foreach( var i in myList ){

Console.WriteLine( i );

}}

}

An implicitly typedvariable declaration

must include an

initialzer

var newValue; // emits error CS0818

var a = 2, b = 1;var x, y = 4;

Not permited

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Chuy i ki d li


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Chuy n i ki u d li uType Conversion (cast)

Nhi u lc c n chuy n i d li u cho c cinstances sang 1 lo i d li u kh c

C 2 d ng chuy n i Implicit cast Explicit cast

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Implicit cast

Tun theo promotion rules. ch c php chuy n ki u n o m khng l m m t

d li u th m i c php

Do C# t th c hi n Khng c n l p tr nh vin can thi p

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Implicit type cast

Xy ra khi p t ki u nh qua ki u l n

p t l p d n xut qua l p c s

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int i = 59;double x = i;

string s = "Hello";object o = s;


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Implicit type-cast

From Tosbyte short, int, long, float, double, decimal

byte short, ushort, int, uint, long, ulong, float, double, decimal

short int, long, float, double, decimal

ushort int, uint, long, ulong, float, double, decimal

int long, float, double, decimal

uint long, ulong, float, double, decimal

long, ulong float, double, decimal

float double

char ushort, int, uint, long, ulong, float, double, decimal

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Explicit type-cast

Do l p tr nh vin ch nh Xy ra khi

p t ki u l n qua ki u nh : c th mt gi tr

p t l p c s qua l p d n xut

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double x = 74.86;int i = ( int ) ) x; // i = 74

string s = "Hello" ;object o = s;string s2 = ( string )o;


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Using Convert class

Th ng dng khi c n chuy n i gi a c c kikhng c lin h v i nhau

Convert.toDataType( SourceValue )

V d : chuy n t chu i sang s th c

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string s1 = "56.8" ;

double x = Convert.ToDouble(s1); // x = 56.8int i = Convert.ToInt32(s2); // i = 95

string s2 = "95" ;

byte j = Convert.ToByte(x); // j = 56, t dng


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System.Object class

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Boxing and unboxing

Dng ch vic chuy n d li u t stack sangheap v ngc l i

M c ch: ci thi n vi c th c thi chng trnh

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Boxing

int i =42;Object o = i;

I is a value type, so it exists in the stack.

O is a reference type, so it must refer toobjects on the heap.

The runtime allocates a piece of memory

from the heap, copies the value of integer i tothis piece, and refers the object o to this copy.

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Boxing

The automatic copying of an item from thestack to the heap is called boxing.

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Boxing

If you modify the original value of a variable,the value on the heap will not change and viceversa.

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Unboxing

Int i=o compile time error. The object o canrefer to absolutely anything and not just anint.

To obtain the value of the boxed copy, youmust use a cast operation

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Unboxing

Int I = 42;Object o = I; //boxesI = (int)o; // compiles okay

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b i


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unboxingCircle c = new Circle(42);Object o = c; // doesnt box because c is a reference

variable;Int I = (int) o; //compiles okay but throws an exception

at run time

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nh hng ca boxing/unboxing n vi c


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nh hng ca boxing/unboxing n vi cth c thi chng trnh

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checked & unchecked


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checked & unchecked

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throws OverFlowException

The checked and unchecked statements areused to control the overflow checking contextfor integral-type arithmetic operations andconversions


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ref , out, param ref: tng t nh truy n tham chi u trong C/C++ T kho ref phi c dng lc g i h m C c tham s truy n d ng ref phi c khi t o gi

tr tr c

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Khai bo ref trckiu d liu

s dng ref chotham s khi gi hm


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ref, out, param

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3 ph n t 6 ph n t Mng array

Lun khaib o cuidanh schtham s


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Keyword this

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public class list{

private int size;

...

public SetSize ( int size ){this.size = size;

}


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Loop

Tng t nh C: while, do while, for

77Phi l gi tr bool: true, false

while < iu kin>{

// phn thn while}

do{

// phn thn do while} while < iu kin>;

for( khi tao bin lp; ; thay i bin lp){

// phn thn for

}


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Loop

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index = 10;while (index != 0){

Console .WriteLine(index);index--;

}

index = 0;do {

Console .WriteLine("Happens at least once");} while (index < 0);

for (index = 0; index < 100; index++){Console. Write(index);Console. Write("\t");

}

Gi tr {true, false}


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foreach

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foreach( typedata identifier in objectArray)

{// thn foreach

}

=

Ch s dng bin icho mi ln lp

S dng ch smng nh bnh

thng


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switch

Bi u th c switch gm: ki u s, k t , enum v chu i

S d ng break, goto, return i u khi n lung th c thi N u ko nh n n o ph hp default N u ko c default th c hi n l nh sau switch

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Jump

break Tho t kh i v ng lp

continue Qua b c lp k

goto Nhy n nh n S d ng goto case , trong switch

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return

Tho t kh i h m void

Tr v 1 gi tr ca h m

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void Func1(int x){

if (x == 0)

return;

...

}

int max(int a, int b){

if (a > b)return a;else

return b;}

Demo


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Demo Rolling a Six-Sided Die

Let us develop an application that simulates20 rolls of a six-sided die and displays thevalue of each roll

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Class Random (of namespace System)

Objects of class Random can producerandom byte, int and double values. A new random-number generator object can

be created as follows:Random randomNumbers = new Random();

The random-number generator object can

then be used to generate random byte, intand double values

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f


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Class Random (of namespace System)

Method Next of class Random generates arandomint randomValue = randomNumbers.Next();

Values returned by Next are actuallypseudorandom numbers a sequence of values produced by a complex mathematicalcalculation.

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C l i bl


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Complex variable types

C# cung c p ba lo i bi n ph c nhng r tthng d ng: Enumerations (often referred to as enums)

structs (occasionally referred to as structures) Arrays

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h gh E i


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nh ngh a Enumeration

Dng t kha enum nh ngh a bi n ki uenumerationsenum {,,,...}

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h gh E i


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nh ngh a Enumeration

M t c ch nh ngh a kh c: d a v o ki u c s(underlying type) lu tr gi tr.

enum :{,,,...

}

Underlying types of byte, sbyte, short, ushort,int, uint, long,and ulong.

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h gh i


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nh ngh a enumeration

Mc nh, m i gi tr c g n cho 1 gi trtng ng v i underlying type value theo tht c nh ngh a c g n gitr 0, c gi tr1

C th override php g n n y b ng to n t =

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Kh i b d ki i


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Khai b o v s d ng ki u enumeration

Khai b o bi n ki u enumeration:;

G n gi trcho bi n: = .;

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St t (h t t )


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Struct (hay structure)

L kiu d li u c hp th nh t nhi u ph nd li u c ki u d li u kh c nhau. Cho php ng i dng t nh ngh a ki u d

li u ca ring m nh.

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h ngh ki t t


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nh ngh a ki u structstruct {}

M i c d ng nh sau: ;

V d : struct route{ public orientation direction;

public double distance;}

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Array

is a collection of values of a similar data type C# arrays are a reference type. Each array in C# is an object and is inherited

from the System.Array class. Arrays are declared as: [] = new []

Ex: int [] integers = new int[10];Hoc: int [] integers;integers = new int[10];

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Array

The size of an array is fixed and must bedefined before using it.

Can use variables to define the size of thearray:

int size = 10;int [] integers = new int[size];

Array can be defined by using the valuesint [] integers = {1, 2, 3, 4, 5};

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Truy xu t c c ph n t mng


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y p gAccessing the values stored in an array

S d ng to n t ch m c (indexing operator)[int index]

Gi tr ch mc trong C# b t u t 0. Truy xu t c c ph n t ca mng:

Dng v ng lp for v to n t ch s Dng v ng lp foreach

Note: v ng lp foreach chcho php read-only.Khng th th c hi n:

foreach (string friendName in friendNames)

{ friendName = "Rupert the bear}; 97

V d 1


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V d 1

static void Main(){

// declaring and initializing an array of type integerint [] integers = {3, 7, 2, 14, 65};for(int i=0; i


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V d 2

static void Main(){

// declaring and initializing an array of type integer

int [] integers = {3, 7, 2, 14, 65};foreach(int i in integers){

Console.WriteLine(i);}

}

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Array


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Array

Ly kch th c mng qua thu c tnh Length int Size = myArray.Length;

N u th nh ph n ca mng l ki u nh tr c,

c th dng h m Sort ca Array s p x p Array.Sort(myArray); Dng h m Reverse ca Array o th t

c c ph n t trong mng Array.Reverse(myArray);

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Array


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Array

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Dng phng thc tnh Sortca lp Array sort artists

Dng phng thc tnh Reverseca lp Array o th t artists

Multidimensional Arrays


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Multidimensional Arrays

A multidimensional array is simply one thatuses multiple indices to access its elements.

C ch khai b o[,,,] ;

V d : t o mng 2 chi u 3 h ng 4 c tdouble[,] hillHeight = new double[3,4];

double[,] hillHeight = { { 1, 2, 3, 4 }, { 2, 3, 4, 5 }, {3, 4, 5, 6 } };

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Multi dimensional Array


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Multi-dimensional Array

Khai b o mng int2 dng 3 c t int[,] myMatrix = new int[2,3];

C th khi g n int[,] myMatrix = new int[,] {{1,2},{3,4},{5,6},{7,8}}; int[,] myMatrix = {{1,2},{3,4},{5,6},{7,8}}; string[,] beatleName = {{"Lennon","John"},

{"McCartney","Paul"},{"Harrison","George"},{"Starkey","Richard"}};

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Datatype[,] array-name


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Multi dimensional Array


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Multi-dimensional Array

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Truy cp tun t theo kiumng1 chiu

Truy cp theo dng dng ctqua ch mc i v j

Jagged Array (Arraysof Arrays)


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Jagged Array (Arraysof Arrays)

Jagged l mng m m i ph n t l m t mng c kcth ckhc nhau

Nh ng mng con n y phi c khai b o ring Khai b o mng3 d ng, m i d ng l m t mng1 chi u

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Datatype[ ][ ] array-name

int[][] a = new int[3][];a[0] = new int[4];a[1] = new int[3];a[2] = new int[1];

Khai bo s dng, hng

Khai bo s ct ring cho tng dng


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Jagged Array


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Jagged Array

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Truy cp theo dng, ct Truy cp dng foreach

Jagged array


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gg y A jagged array cannot be completely created

with a single array creation expression. Ex: int[][] c = new int[ 2 ][ 5 ]; // error

Each one-dimensional array in the jaggedarray must be initialized separately. Ex:int[][] c;

c= new int[ 2 ][ ]; // create 2 rowsc[ 0 ]= new int[ 5 ]; // create 5 columns for row 0c[ 1 ]= new int[ 3 ]; // create 3 columns for row 1

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Demo


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C ch t o mng chu i L m quen 1 s phng thc thng d ng ca

l p string. T o 1 mng m m i ph n t la 1 word trong 1

chuoi duoc nhap vao luc khoi tao lop private string[] myWords;

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String class


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String class

chuong 2 basic c#

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