C# Primer: 实战导向的.NET编程入门指南

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"C#.Primer: A Practical Approach" 是由Stanley B. Lippman撰写的一本实用指南，专为初学者设计，旨在帮助读者快速掌握C#编程语言。这本书采用作者标志性的入门方法，深入浅出地介绍了这个面向对象的新语言。 C#作为微软.NET平台的关键基石，它汲取了Java和C++的诸多优点，被定位为构建高性能Windows和Web应用、组件的强大工具，包括基于XML的Web服务、中间层业务对象以及系统级应用程序。本书引导读者从基础入手，首先通过实例展示来探索C#的核心特性，如类机制、类继承和接口继承，同时在实践中编写小型程序，以便更好地理解和掌握这些概念。书中特别关注以下几个关键点： 1. 基础概念：作者详细讲解了命名空间、异常处理以及统一的类型系统，这些都是C#编程的基础，对于理解和运用语言至关重要。 2. .NET框架库之旅：本书带领读者广泛浏览.NET类库，深入理解ADO.NET，这是用于访问数据库的重要组件。此外，它还展示了如何有效地利用这些库来解决实际问题，构建高质量的软件解决方案。 3. 实战演练：通过丰富的实践项目，读者将有机会应用所学知识，逐步提升编程技能，确保理论与实践的紧密结合。 4. 动态成长：随着.NET平台的发展，C#也在不断进化，书中会紧跟技术潮流，介绍最新的C#特性和框架更新，帮助读者跟上时代的步伐。 "C#.Primer: A Practical Approach" 是一本全面且实用的教程，无论是对编程新手还是经验丰富的开发人员，都能从中受益匪浅，是学习和精通C#的理想入门书籍。通过跟随作者的循序渐进式教学，读者能够迅速建立起坚实的C#编程基础，为进一步的专业发展打下坚实的基础。

conditionally executed; the return statement is executed whether or not the array is

empty.

The

return statement can also return a value. This value becomes the return value of the

function—for example,

public static int Main( string [] args )

{

if ( args.Length == 0 )

{

display_usage();

return -1; // indicate failure

}

The rule is that the value following the return statement must be compatible with the

return type of the function. Compatible can mean one of two things. In the simplest case,

the value being returned is the same type as that indicated as the return type of the

function. The value

-1, for example, is of type int. The second meaning of compatible

requires that an implicit conversion exist between the actual return value and the

function's return type.

The

if-else statement allows us to select between alternative statements on the basis of

the truth of a particular condition. The

else clause represents a statement or statement

block to be executed if the tested condition evaluates to false. For example, if we chose

not to immediately return on discovering an empty

args array, we could provide the

following

if-else statement instead:

if ( args.Length == 0 )

display_usage();

else { /* do everything else here ... */ }

To access the individual command-line options, we'll use a foreach loop to iterate across

the array, reading each element in turn. For example, the following loop statement prints

each option to the user's console:

foreach ( string option in args )

Console.WriteLine( option );

option is a read-only string object. It is visible only within the body of the foreach

statement. Within each iteration of the loop,

option is set to refer to the next element of

the

args array.

For our program, we'll compare each

string element against the set of supported options.

If the string does not match any of the options, we'll check to see if the string represents a

text file. Whenever we are testing a series of mutually exclusive conditions, as we are in

this case, we typically combine the tests into a chain of

if-else-if statements—for

example,

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A second difference between an ordinary and a verbatim string literal is the ability of a

verbatim string literal to span multiple lines. The nested white space within the multiple-

line verbatim string literal, such as a new-line character or a tab, is preserved. This allows

for the storage and generation of formatted text blocks. For example, here is how we

might implement

display_usage():

public void display_usage()

{

string usage =

@"usage: WordCount [-s] [-t] [-h] textfile.txt

where [] indicates an optional argument

-s prints a series of performance measurements

-t prints a trace of the program

-h prints this message";

Console.WriteLine( usage );

}

CreateText() returns a StreamWriter instance. The file represented by the string

argument passed to it, if it exists, is overwritten. To append to a file's existing text rather

than overwriting it, we use

AppendText().

StreamReader provides a collection of read methods allowing us to read a single

character, a block of characters, or, using

ReadLine(), a line of text. (There is also a

Peek() method to read one character ahead without extracting it from the file.)

StreamWriter provides instances of both WriteLine() and Write().

The following code segment reads each line of a text file in turn, assigning it to the string

object

text_line. StreamReader signals that it has reached the end of the file by

returning a

null string. The additional parentheses around the assignment of text_line

are necessary because of what is called operator precedence (see

Section 1.18.4 for a

discussion):

string text_line;

while (( text_line = freader.ReadLine() ) != null )

{

// write to output file

fwriter.WriteLine( text_line );

}

// must explicitly close the readers

freader.Close();

fwriter.Close();

When we finish with the readers, we must invoke their associated Close() member

functions in order to free the resources associated with them.

[6]

If you are a C++ programmer, you are accustomed to having the class destructor automatically free resources. In

a garbage-collected environment, however, destructors cannot provide that service. Rather we provide a

Dispose()

function, which is discussed in Section 4.8

. Close() is an alternative form of Dispose().

1.6 Formatting Output

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