C# - 快速入門 評論   編輯

C# - 概述

C＃是一個現代的，通用的麵向對象的編程語言，由ECMA和ISO批準微軟開發的計算機編程語言。

C＃是由Anders Hejlsberg和他的團隊在開發.Net框架過程中完善出來。

C＃是專為通用語言基礎結構（CLI），其中包括可執行代碼和運行時環境，允許使用的各種高層次的語言要使用在不同的計算機平台和體係結構。

C＃是一種廣泛使用的專業語言理由如下：

• 現代，通用的編程語言

• 麵向對象

• 麵向組件

• 容易學習

• 結構化語言

• 它可生成高效率的程序

• 它可以編譯上的各種計算機平台

• 它是.Net構架的一部分

C#強大的編程功能

雖然C＃構造緊密地遵循傳統的高層次語言C和C++和麵向對象的編程語言，它具有很強的與Java相似，它有許多強大的編程功能，讓眾多世界各地程序員喜愛。

以下是幾個重要的功能列表：

• Boolean條件

• 自動垃圾收集

• 標準庫

• 程序集版本

• 屬性和事件

• 委托和事件管理

• 易於使用泛型

• 索引器

• 條件編譯

• 簡單的多線程

• LINQ和Lambda表達式

• 集成Windows

C＃ - 環境

C＃集成開發環境（IDE）

微軟提供了以下C＃編程的開發工具：

• Visual Studio 2010 (VS)

• Visual C# 2010 Express (VCE)

• Visual Web Developer

最後兩個是可以免費從微軟官方網站。使用這些工具，你可以寫各種C＃程序，從簡單的命令行應用程序更複雜的應用程序。你也可以寫C＃源代碼文件使用一個基本的文本編輯器，如記事本，將代碼編譯成組件使用命令行編譯器，這也是一個.NET框架的一部分。

下調的Visual C＃和Visual Web Developer Express版的Visual Studio版本，並具有相同的外觀和感覺。他們保留了大部分功能的Visual Studio。在本教學中，我們使用Visual C＃2010 Express。

你可以下載 Microsoft Visual Studio. 它會自動安裝在你的機器上。請注意，您需要一個有效的互聯網連接安裝Express版。

在Linux/Mac OS上寫C#程序

雖然NET Framework運行在Windows操作係統中，也有一些替代版本，也可以在其他操作係統上工作。 Mono是一個開放源碼的版本.NET框架，其中包括C＃編譯器和運行於多個操作係統，包括Linux和Mac OS等其它係統。請查看Go Mono.

Mono的目的不僅要能夠運行微軟.NET應用程序的跨平台，但也帶來更好的開發工具，Linux開發人員。 Mono可以運行在多種操作係統上，包括Android，BSD，IOS，Linux操作係統，OS X時，Windows，Solaris和UNIX。

C# - 程序結構

C# Hello World 示例

C＃程序基本上由以下幾部分組成:

• 命名空間聲明

• 一個類

• 類方法

• 類屬性

• Main方法

• 語句和表達式

• 注釋

讓我們來看看一個簡單的代碼，將打印“Hello World”：

using System;
namespace HelloWorldApplication
{
   class HelloWorld
   {
      static void Main(string[] args)
      {
         /* my first program in C# */
         Console.WriteLine("Hello World");
         Console.ReadKey();
      }
   }
}

上麵的代碼編譯和執行時，它會產生以下結果：

Hello World

讓我們來看看上麵的程序的各個部分：

• The first line of the program using System; - the using keyword is used to include the System namespace in the program. A program generally has multiple using statements.

• The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld.

• The next line has a class declaration, the class HelloWorld, contains the data and method definitions that your program uses. Classes generally would contain more than one method. Methods define the behavior of the class. However, the HelloWorld class has only one method Main.

• The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class will do when executed

• The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program.

• The Main method specifies its behavior with the statement Console.WriteLine("Hello World");

  WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen.

  
  

• The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET.

這是值得大家注意以下幾點：

• C#是大小寫敏感的.

• All statements and expression must end with a semicolon (;).

• The program execution starts at the Main method.

• Unlike Java, file name could be different from the class name.

Compile & Execute a C# Program:

If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps:

• Start Visual Studio.

• On the menu bar, choose File, New, Project.

• Choose Visual C# from templates, and then choose Windows.

• Choose Console Application.

• Specify a name for your project, and then choose the OK button.

• The new project appears in Solution Explorer.

• Write code in the Code Editor.

• Click the Run button or the F5 key to run the project. A Command Prompt window appears that contains the line Hello World.

You can compile a C# program by using the command line instead of the Visual Studio IDE:

• Open a text editor and add the above mentioned code.

• Save the file as helloworld.cs

• Open the command prompt tool and go to the directory where you saved the file.

• Type csc helloworld.cs and press enter to compile your code.

• If there are no errors in your code the command prompt will take you to the next line and would generate helloworld.exe executable file.

• Next, type helloworld to execute your program.

• You will be able to see "Hello World" printed on the screen.

C# - Basic Syntax

C# is an object oriented programming language. In Object Oriented Programming methodology a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, more often, are said to be in the same class.

For example, let us consider a Rectangle object. It has attributes like length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating area and display details.

Let us look at an implementation of a Rectangle class and discuss C# basic syntax, on the basis of our observations in it:

using System;
namespace RectangleApplication
{
    class Rectangle
    {
        // member variables
        double length;
        double width;
        public void Acceptdetails()
        {
            length = 4.5;    
            width = 3.5;
        }
        public double GetArea()
        {
            return length * width;
        }
        public void Display()
        {
            Console.WriteLine("Length: {0}", length);
            Console.WriteLine("Width: {0}", width);
            Console.WriteLine("Area: {0}", GetArea());
        }
    }
    
    class ExecuteRectangle
    {
        static void Main(string[] args)
        {
            Rectangle r = new Rectangle();
            r.Acceptdetails();
            r.Display();
            Console.ReadLine();
        }
    }
}

When the above code is compiled and executed, it produces following result:

Length: 4.5
Width: 3.5
Area: 15.75

The using Keyword

The first statement in any C# program is

using System;

The using keyword is used for including the namespaces in the program. A program can include multiple using statements.

The class Keyword

The class keyword is used for declaring a class.

Comments in C#

Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below:

/* This program demonstrates
The basic syntax of C# programming 
Language */

Single line comments are indicated by the '//' symbol. For example,

}//end class Rectangle    

Member Variables

Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width.

Member Functions

Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetails, GetArea and Display.

Instantiating a Class

In the preceding program, the class ExecuteRectangle is used as a class which contains the Main() method and instantiates the Rectangle class.

Identifiers

An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in C# are as follows:

• A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.

• It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However an underscore ( _ ) can be used.

• It should not be a C# keyword.

C# - Data Types

In C#, variables are categorized into the following types:

• Value types

• Reference types

• Pointer types

Value Types

The following table lists the available value types in C# 2010:

Type	Represents	Range	Default Value
bool	Boolean value	True or False	False
byte	8-bit unsigned integer	0 to 255	0
char	16-bit Unicode character	U +0000 to U +ffff	'\0'
decimal	128-bit precise decimal values with 28-29 significant digits	(-7.9 x 1028 to 7.9 x 1028) / 100 to 28	0.0M
double	64-bit double-precision floating point type	(+/-)5.0 x 10-324 to (+/-)1.7 x 10308	0.0D
float	32-bit single-precision floating point type	-3.4 x 1038 to + 3.4 x 1038	0.0F
int	32-bit signed integer type	-2,147,483,648 to 2,147,483,647	0
long	64-bit signed integer type	-923,372,036,854,775,808 to 9,223,372,036,854,775,807	0L
sbyte	8-bit signed integer type	-128 to 127	0
short	16-bit signed integer type	-32,768 to 32,767	0
uint	32-bit signed integer type	0 to 4,294,967,295	0
ulong	64-bit signed integer type	0 to 18,446,744,073,709,551,615	0
ushort	16-bit signed integer type	0 to 65,535	0

Reference Types

The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.

In other words, they refer to a memory location. Using more than one variable, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built in reference types are: object, dynamic and string.

Object Type

The Object Type is the ultimate base class for all data types in C# Common Type System(CTS). Object is an alias for System.Object class. So object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type it is called unboxing.

object obj;
obj = 100; // this is boxing

Dynamic Type

You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at runtime.

Syntax for declaring a dynamic type is:

dynamic <variable_name> = value;

For example,

dynamic d = 20;

Dynamic types are similar to object types except that, type checking for object type variables takes place at compile time, whereas that for the dynamic type variables take place at run time.

String Type

The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.

For example,

String str = "Tutorials Point";

A @quoted string literal looks like:

@"Tutorials Point";

The user defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.

Pointer Types

Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as in C or C++.

Syntax for declaring a pointer type is:

type* identifier;

For example,

char* cptr;
int* iptr;

C# - Type Conversion

Type conversion is basically type casting, or converting one type of data to another type. In C#, type casting has two forms:

• Implicit type conversion - these conversions are performed by C# in a type-safe manner. Examples are conversions from smaller to larger integral types, and conversions from derived classes to base classes.

• Explicit type conversion - these conversions are done explicitly by users using the pre-defined functions. Explicit conversions require a cast operator.

C# Type Conversion Methods

C# provides the following built-in type conversion methods:

S.N	Methods & Description
1	ToBoolean Converts a type to a Boolean value, where possible.
2	ToByte Converts a type to a byte.
3	ToChar Converts a type to a single Unicode character, where possible.
4	ToDateTime Converts a type (integer or string type) to date-time structures.
5	ToDecimal Converts a floating point or integer type to a decimal type.
6	ToDouble Converts a type to a double type.
7	ToInt16 Converts a type to a 16-bit integer.
8	ToInt32 Converts a type to a 32-bit integer.
9	ToInt64 Converts a type to a 64-bit integer.
10	ToSbyte Converts a type to a signed byte type.
11	ToSingle Converts a type to a small floating point number.
12	ToString Converts a type to a string.
13	ToType Converts a type to a specified type.
14	ToUInt16 Converts a type to an unsigned int type.
15	ToUInt32 Converts a type to an unsigned long type.
16	ToUInt64 Converts a type to an unsigned big integer.

The following example converts various value types to string type:

namespace TypeConversionApplication
{
    class StringConversion
    {
        static void Main(string[] args)
        {
            int i = 75;
            float f = 53.005f;
            double d = 2345.7652;
            bool b = true;

            Console.WriteLine(i.ToString());
            Console.WriteLine(f.ToString());
            Console.WriteLine(d.ToString());
            Console.WriteLine(b.ToString());
            Console.ReadKey();
            
        }
    }
}

When the above code is compiled and executed, it produces following result:

75
53.005
2345.7652
True

C# - Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C# has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

We have already discussed various data types. The basic value types provided in C# can be categorized as:

Type	Example
Integral types	sbyte, byte, short, ushort, int, uint, long, ulong and char
Floating point types	float and double
Decimal types	decimal
Boolean types	true or false values, as assigned
Nullable types	Nullable data types

C# also allows defining other value types of variable like enum and reference types of variables like class, which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.

Variable Declaration in C#

Syntax for variable declaration in C# is:

<data_type> <variable_list>;

Here, data_type must be a valid C# data type including char, int, float, double, or any user defined data type etc., and variable_list may consist of one or more identifier names separated by commas.

Some valid variable declarations along with their definition are shown here:

int i, j, k;
char c, ch;
float f, salary;
double d;

You can initialize a variable at the time of declaration as:

int i = 100;

Variable Initialization in C#

Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is:

variable_name = value;

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as:

<data_type> <variable_name> = value;

Some examples are:

int d = 3, f = 5;    /* initializing d and f. */
byte z = 22;         /* initializes z. */
double pi = 3.14159; /* declares an approximation of pi. */
char x = 'x';        /* the variable x has the value 'x'. */

Lvalues and Rvalues in C#:

There are two kinds of expressions in C#:

1. lvalue : An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.

2. rvalue : An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement:

int g = 20;

But following is not a valid statement and would generate compile-time error:

10 = 20;

C# - Constants and Literals

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer Literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals:

212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */
078         /* Illegal: 8 is not an octal digit */
032UU       /* Illegal: cannot repeat a suffix */

Following are other examples of various types of Integer literals:

85         /* decimal */
0213       /* octal */
0x4b       /* hexadecimal */
30         /* int */
30u        /* unsigned int */
30l        /* long */
30ul       /* unsigned long */

Floating-point Literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

Here are some examples of floating-point literals:

3.14159       /* Legal */
314159E-5L    /* Legal */
510E          /* Illegal: incomplete exponent */
210f          /* Illegal: no decimal or exponent */
.e55          /* Illegal: missing integer or fraction */

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Character Constants

Character literals are enclosed in single quotes e.g., 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').

There are certain characters in C# when they are proceeded by a back slash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here you have a list of some of such escape sequence codes:

Escape sequence	Meaning
\\	\ character
\'	' character
\"	" character
\?	? character
\a	Alert or bell
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\v	Vertical tab
\ooo	Octal number of one to three digits
\xhh . . .	Hexadecimal number of one or more digits

字串常值

字符串文字或常量括在雙引號“”@“”。一個字符串包含的字符，字符文字：普通字符，轉義序列和通用字符。

您可以將一個長行成多行字符串和分離的部分用空格。
下麵是一些例子不同的字符串。所有這三種形式是相同的字符串。

"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
@"hello dear"

定義常量

使用const關鍵字定義常量。定義一個常量的語法是：

const <data_type> <constant_name> = value;

C#快速入門（二）
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