VB2008从入门到精通(PDF格式英文版)-第30章
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End If
End Sub
Notice how the first Date。Parse（） processed English…Canadian formatted text and knew
that the identifier May equaled the fifth month of the year。 For the second Date。Parse（） method
call； the culture was changed to German； and it was possible to process 10 Mai； 2008。 In both
cases； processing the buffer posed no major problems； as long as you knew that the buffer was
a German or English…Canadian date。 Where things can go awry is when you have a German
date and an English culture。
Converting a data type to a buffer is relatively easy because the ToString（） methods have
been implemented to generate the desired output。 Consider the following example； which
generates a buffer from an integer value：
Public Sub TestGenerateString（）
Dim iValue As Integer = 123
Dim buffer As String = iValue。ToString（）
If buffer = 〃123〃 Then
Console。WriteLine（ 〃correct〃）
End If
End Sub
In the example； the value 123 has been assigned to iValue； which is of type Integer； and
then its ToString（） method is called； which generates a buffer that contains 〃123〃。 The same
thing can be done to a Double value； as in this example：
Dim number As Double = 123。5678
Dim buffer As String = number。ToString（〃0。00〃）
Here； the number 123。5678 is converted to a buffer using the ToString（） method； but
ToString（） has a parameter； which is a formatting instruction that indicates how the double
number should be generated as a buffer。 The desired result is a buffer with a maximum of two
digits after the decimal point。 Because the third digit after the decimal is a 7； the value is
rounded up； resulting in the buffer 123。57。
Let’s see an example where the culture information also applies to generating a buffer。
Here； a Double value is generated in the format of the culture：
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74 CH AP T E R 3 ■ L E A R N IN G AB OU T ST R I N G M A N I P U L AT IO N S
Public Sub TestGenerateGermanNumber（）
Dim number As Double = 123。5678
Thread。CurrentThread。CurrentCulture = _
new CultureInfo（〃de…DE〃）
Dim buffer As String = number。ToString（〃0。00〃）
If buffer = 〃123；57〃 Then
Console。WriteLine（ 〃correct〃）
End If
End Sub
As in the previous examples； the CurrentCulture property is assigned the desired culture。
Then when the Double variable number has its ToString（） method called； the buffer 〃123；57〃
is generated。
The Important Stuff to Remember
In this chapter； you learned about strings and writing code。 Here are the keys points to
remember：
o Writing tests is an important part of your development practice。 A test is not just a mech
anism to catch errors； but also a mechanism used to understand the dynamics of your code。
o The String type is a special reference type that has many methods and properties。 You
are advised to look at the MSDN documentation to see what a string can do。
o IntelliSense and the MSDN documentation are your best bets when you want to find out
about specific methods； properties； or types。 Books and web sites such as Code Project
are good resources to help you understand concepts。
o All variables and types are based on the object type。
o When writing code； you need to define responsibilities and contexts。 Don’t fix bugs or
write code using knee…jerk reactions。
o All strings are based on Unicode。 Each Unicode character is 16 bits wide。
o When translating buffers； you need to deal with the translation of text and the translation of
numbers and dates。
o includes sophisticated technology to help you translate numbers and dates using a
bination of language and culture information。
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CH AP T E R 3 ■ L E AR N IN G AB O U T ST R I N G M A N I PU L A TI O N S 75
Some Things for You to Do
The following are some exercises that relate to what you’ve learned in this chapter。
1。 Finish the application to translate from one language to another language； allowing the
user to choose which direction the translation takes。
2。 Extend the LanguageTranslator ponent to be able to translate the words au revoir
and auf wiedersehen to good bye。
3。 You can bine strings by using the plus sign； but doing many additions will slow
down your code。 Use the StringBuilder class to concatenate two buffers together。 Hint：
you want to convert the code String c = a ＋ b； and make a and b use the StringBuilder
class。 The result of the StringBuilder is assigned to the variable c。
4。 Create a test that demonstrates what happens when a number value is added to a string
value。 Write the appropriate tests to verify your conclusion。
5。 Extend the LanguageTranslator ponent to include methods to translate English
numbers into German numbers。
6。 Extend the LanguageTranslator ponent to include methods to translate dates from
American or Canadian dates into German dates。 Note that the added wrinkle is that you
could input an American or Canadian date。
7。 Implement the Windows application that calls the LanguageTranslator ponent。
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C H A P T E R 4
■ ■ ■
Learning About Data Structures；
Decisions； and Loops
When you are creating applications； the source code will need to make decisions； such as
should you open the file or save the file？ And if you open the file； what kind of iterative code is
going to read the contents of the file？ These sorts of questions are answered by employing data
structures； decisions； and loops。
The easiest way to demonstrate how to make a decision is to write a miniature artificial
intelligence （AI） system。 The AI system will be extremely primitive； but AI is interesting because
it makes extensive use of decision and loop constructs。 The AI system iterates and makes deci
sions based on data defined in a neat and orderly custom data structure。
Using the example of creating an algorithm； the following topics will be covered in this
chapter：
o Data structures； including custom types
o The restrictions of value types
o Algorithm design
o Class constructors； which allow you to initialize an object
o The For loop； which allows you to iterate over sets of data
o The If statement； which allows you to execute specific code based on logic
Understanding the Depth…First Search Algorithm
AI involves searching for data； and a core algorithm of AI is searching。 The search algorithm
that we will develop for this chapter’s example is a depth…first search system。 AI has other types
of searches； such as an A* or a breadth…first search； but they are all based on the same idea as
the depth…search algorithm。 This idea is searching for information that is arranged in a tree
structure。
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78 CH AP T E R 4 ■ L E A R N IN G AB OU T D AT A S TR
