lesson 5 pp
TRANSCRIPT
Microsoft Visual Basic 2005 BASICS
Lesson 5
Data Types and Variables
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Objectives
Describe the purpose of data types and variables.
Use the AutoSize property. Declare and use variables. Describe the scope of variables. Describe the Object data type.
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Data Types
Computers are all about data. Visual Basic supports a certain set of
data types. You can choose to store data in memory
locations called variables. Variables
Can be used to store and manipulate all kinds of data
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Data Types (cont.)
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Using the AutoSize Property
The AutoSize property Adjusts the size of a control to fit its
contents Label control example
The AutoSize property will shrink or enlarge the label to fit the text.
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Using the AutoSize Property (cont.)
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Using the AutoSize Property (cont.)
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Declaring Variables
Using a variable in your programs Let the compiler know
That you want to set up a memory location as a variable
What you want to call the variable What data type you want the variable to
have
Declare a variable Use the Dim statement
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Rules for Naming Variables
When naming variables, keep the following rules in mind: Variable names must begin with an
alphabetic character. Following the first character, letters,
numbers, and underscores are allowed. Variable names cannot include spaces. Variable names can be 255 characters
long.
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Rules for Naming Variables (cont.)
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Using Variables
Variables can be used in the same way as labels and text boxes.
Use the assignment operator to assign a value to a variable. You can also assign hard-coded values to
a variable.
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Using Variables (cont.)
Use mathematical operators to perform calculations with numeric variables.
Output the value in a variable. Assign the value to a label.
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Using Variables (cont.)
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Using Variables (cont.)
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Scope
The term “scope” refers to the reach of a variable.
General rule You should declare variables as locally as
possible.
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Three Levels of Scope
Levels Local variable
Declared within an event procedure Form-level variable
Declared in the Declarations section of a form’s Code window
Global variable Declared in a code module’s section
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The Declarations Section
Access the Declarations section Select (Declarations) from the Method
Name list that appears at the top of the Code window.
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The Declarations Section (cont.)
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The Declarations Section (cont.)
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Using the Object Data Type
Object data type Very flexible Can store many different types of variables
Object variables Can be declared by specifying the Object
type Or by declaring a variable without a type
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Summary
Data can be in the form of numbers, text, dates, pictures, and even sound.
Visual Basic supports a set of data types. There are data types for whole numbers, floating-point numbers (decimals), text, dates, and more.
You can choose to store data in memory locations called variables.
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Summary (cont.)
The AutoSize property will adjust the size of a control to fit its contents.
The first step to using a variable is to declare it using the Dim statement.
When naming variables, keep the naming rules in mind. It is a good idea to use naming prefixes to identify the data type of the variable.
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Summary (cont.)
You can assign values to variables using the assignment operator. You can also use the other mathematical
operators with numeric variables. A variable’s scope indicates the
procedures that have access to the variable. A variable’s scope can be local, form-level, or global.
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Summary (cont.)
The Declarations section of a form’s Code window allows you to declare form-level variables.
The Object data type can hold many different kinds of data, but is less efficient than specific data types.