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speaking; in the source code category; each thought corresponds to a feature to implement。
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Figure 2…1。 Brainstorming what the calculator application represents
Figure 2…2。 Focused and organized brainstorming
Focusing the Calculator
To implement a feature; you need source code; which means a file; project; and other program
ming techniques。 The following two levels of organization are defined in Visual Basic:
o File level: At the file level; you are organizing what kinds of projects and solutions you
will be creating。
o Source code level: At the source code level; you are organizing the namespaces; modules;
class names; and other identifiers that are referenced throughout the source code。
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28 CH AP T E R 2 ■ L E A R N IN G AB OU T 。 N E T N U M B E R A N D V A L U E T Y P E S
For the most part; Visual Basic developers do not concern themselves too much with the
file organization。 A mon practice is to consider a class or module as a single file。
When implementing an application; you will begin by deciding whether you will use a
console application; a Windows application; or a class library。
If the calculator were a Windows application; it could look like Figure 2…3。 A calculator
implemented as a Windows application allows users to perform calculations by clicking the
appropriate buttons。 For example; to add two numbers; the user clicks the appropriate buttons
to key in the first number; then an operation; then the second number; and finally; the equal
sign to perform the calculation。 The equal sign is a signal to the calculator application to process
the data that has been entered and generate a result。 The text box would display the results。
Figure 2…3。 A calculator implemented as a Windows application
The second choice is to implement a calculator using a console application; where the
numbers are entered as text; as illustrated in Figure 2…4。 The calculator does not expect users to
click buttons; rather; they press the appropriate keyboard keys to enter the appropriate number at
the appropriate time with the appropriate operation。 Typically; an Enter key will serve as an
equal sign button and perform a calculation; which is output to the console。 Once one calcula
tion has pleted; the cycle starts again。
If you had to choose between a Windows or console application for the calculator; you would
choose the Windows application because it looks better and is easier to use。 In the focused
thoughts of Figure 2…2; ease of use was not defined as a feature。 Should the user interface type have
been a feature? Normally; yes it should be a feature; but for the scope of this chapter; it is not。
The user interaction between the two types of applications is dramatically different; and
implies two different programs; even though they implement the same features。 The focus is
not on creating a particular program type; but on the overall programming structure。
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Figure 2…4。 A calculator implemented as a console application
Let’s step back and think about this abstractly。 You are a programmer and have been
charged with the task of implementing the calculator for both user interfaces。 Again; thinking
abstractly; would you implement all the functionality twice; or would you try to think about
which parts of the calculator could be reused for both user interfaces? Most likely; your answer
will be that you want to reuse parts of the calculator so that you have less work。 But you also want
to reuse parts so that you can avoid additional maintenance and program extension problems。
So; for software development; you need to think of the software as pieces that are assem
bled into a program。 Some pieces can be reused; and other pieces cannot be reused。 Therefore;
think of the calculator application as two pieces: the user interface and the piece that performs
calculations based on data delivered by the user interface。 From an organizational perspective;
or in developer lingo; from an architectural perspective; the calculator pieces would be arranged as
shown in Figure 2…5。
The individual pieces in Figure 2…5 are called ponents。 (Some individuals might even
call the pieces modules; but I personally prefer the term ponents; and in a Visual Basic
book; calling them modules could lead to confusion)。 The ponents are arranged from the
lower…level functionality at the bottom of the picture to the higher…level functionality near the
top of the picture。
Each ponent fulfills a particular task; and the higher…level ponents use those tasks
implemented at a lower level。 The idea is that each level is responsible for certain functionality;
and other levels do not duplicate efforts by reimplementing certain functionality。 The higher
level functionality does have a lower…level dependency; but the lower level does not have a
higher…level dependency。
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30 CH AP T E R 2 ■ L E A R N IN G AB OU T 。 N E T N U M B E R A N D V A L U E T Y P E S
Figure 2…5。 Arrangement of calculator pieces
Applications are realized using either top…down or bottom…up architecture。 A top…down
methodology means creating the higher…level ponents and then implementing the lower
level ponents when needed。 In contrast; a bottom…up methodology means creating the
bottom ponents first。
A bottom…up approach is useful when you know clearly which features need to be imple
mented。 A top…down approach is better when you have a rough idea of what features need to
be implemented; but don’t want to stray too far from the goal of the application。 The focus of
this chapter is to develop the Calculator class library; shown at the bottom of Figure 2…5; so we
will take the bottom…up approach in this chapter。
Implementing the Class Library
The creation of a class library is a form of file organization。 The next step is to create some
source code for the class library。 The source code is implemented in two steps:
o Define the class and methods。
o Implement the methods。
One of the biggest problems when learning a new language is understanding what the
language can and cannot do。 You can’t write source code that the language does not under
stand。 So it is extremely important to know the programming language; because it determines
how your thoughts will be structured。
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You will write two types of source code: source code that organizes and source code that
does something。 Organizational source code is like a filing system with folders。 Source code
that does something is like a folder with stuff in it。 When you are creating the filing sy