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.