Bài giảng Lập trình trên Windows - Chương 1: C# cơ bản

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C# cơ bản

.Net framework

Mechanism

Hello world

Artifact

❑ Build => Error

❑ Run vs Run without debugging

❑ Release

❑ Debug

▪ Breakpoint & watch

▪ Step in & Step over

▪ Watch

❑ Set as startup project

❑ Open project location

Types

Variable

int i; // Simple variable

// Many variables can have the same type declaration

float x, y, z;

byte x = 1, y, z = 3;

string name = "new name";

// Array: Indexed by an integer from Zero

int x[] = {1, 2, 3};

// compile error

int[] x = {1, 2, 3}; char[] y = new char[6]; // OK

int x1 = x[0];

// 1

// Multi dimension array: same size in all item

int [,] x = {{1, 2}, {3, 4}};

int [,] x = {{1, 2}, {3, 4, 5}};

int x2 = x[1, 0];

// compile error

// 3

int [,,] x = {{{1, 2}, {3, 4}}, {{5, 6}, {7, 8}}};

Number casting

// Smaller type in memory size integral

// type to wider one

byte b = 5; // implicit int to byte

int i = b; // i = 5

// Wider integral type to smaller one

int i = 500;

byte j = i; // compile error

byte j = (byte)i; // i = 244

// No explicit conversion for floating

// point number

Boxing / Unboxing

❑ Boxing: convert value type to object

❑ Unboxing: extract value type from object

Minimum & maximum value

Result?

Operation 1/2

❑ References: . () [] new ->

❑ Arithmetic: + ++ - -- * / % sizeof

❑ Logical: & | ^ !

❑ Conditional: && (&) || ! == != > >= < <=

❑ Type verification: is as typeof

❑ Bitwise: ~ >> <<

❑ Assignment: = += -= *= /= %= &= |=

^= >>= <<=

❑ Selection: ?: ?? (not null)

❑ Lambda expression definition: =>

Operation 2/2

int i = 5;

// Selection ?:

string x = i == 5 ? "Yes": "No";

int? x = 5;

int y = x ?? 0; // Selection ?? operator

int z = x; // Error: nullable type

// nullable type

// cannot assign to non-nullable type

// Lambda expression – anonymous method

(int x) => x * 2; <=>

public int Double(int x){return x * 2}

String literal

// Declaration and initialization

// "\" start an "escape" code

string s1 = "a\n", s2 = "\"",

s3 = @"a\n", s4 = s3;

// assignment

s2 = s1;

// concatenation

s3 = s1 + s3;

Escape code

\a Bell (alert)

\b Backspace

\f Formfeed

Single quotation mark

Double quotation mark

Backslash

\n New line

Literal question mark

ASCII character in

octal notation

\r Carriage return \ooo

ASCII character in

hexadecimal notation

\t Horizontal tab \x hh

\v Vertical tab

\x hhhh Unicode in herxadeximal

String Format

string header = String.Format(

"{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",

// pattern string

"City", "Year", "Population", "Change (%)"); // argument list

string body = String.Format(

"{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",

Name, BaseYear, BasePopulation, ObserveYear, ObservePopulation,

ObservePopulation – BasePopulation)/ (double) BasePopulation);

// Sample output

City

Year Population

Change (%)

------------------------------------------------------------------

Los Angeles

New York

Chicago

1940

1,504,277

7,454,995

3,396,808

1,623,452

1950

1,970,358

7,891,957

3,620,962

1,849,568

31.0 %

5.9 %

6.6 %

Detroit

13.9 %

string s = $"{x} - {y}";

String concatenation

❑ Use “+” character

❑ Use StringBuilder

❑ Question: what should we use, + or StringBuilder?

String Split

❑ Exercise

▪ Calculate sum of string numbers = “5, 3, 8, 11, -12, 3”

▪ Split String fraction = “3/4” into int numerator and

denominator

What if we meet 3//4?

String format

❑ Positive: right align, negative: left align

String search

❑ Exercise

▪ Given string s = “She sells seashells by the seashore.

The shells she sells are seashells”

▪ Calculate the number of occurrence of the word

“sells” and “she”

❑ Further reading: replace and regular expression

String as char array

Faster!

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