Representing Data: Constants and Variables

CHAPTER THREE

Matakuliah : T0063 – Pemrograman VisualTahun : 2009

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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

• (Name)• AcceptButton• BackColor• CancelButton• ControlBox

• Font• MaximizeBox• MinimizeBox• Text

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Form as a Class

• 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.