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bottom…up。
o Within an architecture； individual pieces are called ponents； and they fit together to
create a plete application。
o You write tests because you cannot verify the functionality of a ponent based on its
identifier； parameters； or return value。
o When implementing ponents； you develop tests before； during； and after writing
the source code。
o A test is a piece of source code that calls a ponent using targeted input data； and the
results from the ponent are verified with targeted responses。 If the results do not
match the targeted responses； the ponent has failed。
o The CLR offers many different data types； with the major distinction being between
value and reference types。
o The CLR has many different number types； but all number types are value types。
o Numbers can overflow or underflow。 You should activate a piler setting to make
sure that the CLR will catch those situations。
o When deciding on a specific number type； a large part of the decision is based on how
much precision is desired。
Some Things for You to Do
The following are some things to consider related to what you’ve learned in this chapter：
1。 When you write code； how should you organize your code？ For example； do you enforce
certain naming conventions for your classes？ Do you enforce the use of code ments？
2。 In the development munity； there is a discussion of whether organization of your
software should involve formal structures or should be ad hoc。 Think about how software
should be organized。
3。 In general； how would you test whether or not a ponent that uses a database worked
properly？ Outline the process with bulleted points。
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4。 In general； how would you test the correctness of writing data to a file？ To help under
stand the nature of the problem； how do you know that an operating system manipulates
files properly？
5。 If the CLR did not provide for a mechanism to catch overflow and underflow conditions；
how would you ensure that overflow and underflow didn’t happen？
6。 For a Pentium CPU （32 bits）； which number type would result in the fastest calculations？
7。 In this chapter’s example； the class Operations is designed to perform arithmetic using
the Double type。 How would you change this so that the calculations are generic and
don’t rely on the Double type？
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C H A P T E R 3
■ ■ ■
Learning About String
Manipulations
In the previous chapter； you learned the basics of how data is stored and managed by ；
including the difference between value and reference types。 has three major data types：
number…related； custom…defined； and String。 The previous chapter focused on the number
related types。 This chapter will focus on the String type。
As you’ll learn in this chapter； the String type has some special characteristics。 If you were
to look at the bits and bytes of the String type； you would not realize that they were letters。 In
an abstract description； a String type is a number type with a special grammar。 Since a puter
understands only numbers； it uses lookup tables that map a set of letters to a set of numbers。
The example in this chapter is a multilingual translation program。 The translation program
will not be sophisticated； nor will it be capable of much。 However； it will illustrate many of the
issues that you will be confronted with when working with strings。
Organizing the Translation Application
As emphasized in the previous chapter； the first step in developing an application is to get
organized。 We need to understand and define the features of the sample application we are
going to develop。 The multilingual translation program will implement the following features：
o Translate greetings into three different languages： French； German； and English。
o Convert numbers into the three different languages。
o Convert a date into the three different languages。
From a feature perspective； the first feature is logical； but the second and third features are
not as obvious。 We generally think of translation as translating one word to another word（s）。
Yet； languages also can represent numbers and dates in different ways。 Translation will mean
two things： translate a word from one language to another； and translate a number or date
from one language to another。
As in Chapter 2； we’ll create the solution as ponents with three pieces： a Windows
application； a testing console application； and a class library。 After you have created each of the
projects； your workspace should look like Figure 3…1。 Remember to add a reference to the
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52 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
LanguageTranslator class library （right…click TestLanguageTranslator and choose Add Reference
Projects LanguageTranslator）。 Also remember to set TestLanguageTranslator as the
startup project。
Figure 3…1。 Structure of projects for the translation application in Visual Basic Express
Solution Explorer
Building the Translator Application
The translation application； like the calculator application example in the previous chapter； is
built in pieces： the class library that performs translations based on data delivered by the user
interface； the tests； and the user interface。 The individual pieces are ponents that can be fit
together like a jigsaw puzzle to create an application。
■Note ponents are a core part of your development toolbox。 As you will see throughout the book；
ponents allow you to reuse and modularize functionality。 ponents result in applications that are main
tainable and extendable。 Of course； there are limits； and the advantages are not automatic。 You will need to
properly design your application to benefit from using ponents。
Creating the Translator Class
When working with Visual Basic Express； or one of the other Visual Studio products； using the
default templates for creating a class library results in the creation of a file named Class1。vb。 It
is good that a default file is created for a class library； but the identifier Class1。vb does not imply
much。 Therefore； you should go ahead and delete that file from the project （simply renaming
the file does not rename the class within it）。 In its place； create the Translator class； as follows：
1。 Right…click the LanguageTranslator project。
2。 Click Add New Item。
3。 Select Class。
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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 53
4