Matakuliah
Tahun
: T0063 – Pemrograman Visual
: 2009
Representing Data: Constants and Variables
CHAPTER THREE
Chapter Introduction
• Compose event procedures that perform more
sophisticated tasks.
• Focus specifically on data items.
• Continue work with Visual Basic .NET project structure.
• Determine the meaning of the term scope.
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Objectives
• Differentiate between numeric and string data.
• Determine whether a data item should be a constant or
variable.
• Code constants and variables in event procedures.
• Describe the characteristics and uses of standard data
types.
• Create projects that consist of several forms.
• Explain scope and describe the domain of variables in
procedures and forms.
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3.1 Data Categorization
• Two broad categories of data are numeric and string.
– Numeric data must contain only numbers.
– String data can contain any symbol.
– Numeric data is used in arithmetic calculations.
– String data cannot be used in calculations.
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3.2 Constants
• Data item whose value is assigned at design time and
remains the same at run time.
• A literal constant is just a value.
• A symbolic constant is a descriptive name substituted for
a literal constant.
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Standard Data Types
• Number of Bytes
– Main memory occupied by a variable.
• Range
– Largest and smallest values that can be stored in a
numeric variable of a given type.
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Standard Data Types (cont.)
• Precision
– Indicates how close together two numeric values can
be.
• Speed of Arithmetic Calculation
– Differs for the different data types.
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Choosing the Best Data Type
for a Variable
• Use decision rules
– Ex. Boolean is the best type for a variable that may be true or
false.
– Ex. Decimal is the best type for a dollar amount.
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Declaring Variables:
The Dim Statement
• A variable declaration statement.
– Examples:
• Dim StreetAddress As String
• Dim GrossWeight As Integer
• Dim HomePhone As String
• Dim NetIncome As Decimal
• Dim CurrentStudent As Boolean
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Using Variables:
The Assignment Statement
• Syntax of the Assignment Statement
– variablename = expression
• Ex. CourseCode = “CISB119”
• Run Time: The Effect of the Assignment Statement
– Evaluates expression on right side of equal sign.
– Stores value of expression in variable on left side of
equal sign.
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Appearance and Use
• Multiple forms may be used for large projects.
– Each form should represent an objective.
– Each form should be clear and attractive.
• Each form is a user interface window during run time.
• All forms have the same basic components.
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Properties of the Form Control
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(Name)
AcceptButton
BackColor
CancelButton
ControlBox
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Font
MaximizeBox
MinimizeBox
Text
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Form as a Class
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You create a class template by creating a form.
Buttons and text boxes are added to the class definition.
Events are methods added to the form class.
Many properties and methods are inherited from the
form’s superclass.
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