Microsoft Visual Basic 2005 BASICS yo Microsoft Visual Basic 2005 BASICS Lesson 5 Data Types and Variables

Objectives Describe the purpose of data types and variables. yo 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. Microsoft Visual Basic 2005 BASICS

Data Types Computers are all about data. yo 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 Microsoft Visual Basic 2005 BASICS

Data Types (cont.) Microsoft Visual Basic 2005 BASICS

Using the AutoSize Property yo 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. Microsoft Visual Basic 2005 BASICS

Using the AutoSize Property (cont.) Microsoft Visual Basic 2005 BASICS

Using the AutoSize Property (cont.) Microsoft Visual Basic 2005 BASICS

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 Microsoft Visual Basic 2005 BASICS

Rules for Naming Variables yo 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. Microsoft Visual Basic 2005 BASICS

Rules for Naming Variables (cont.) Microsoft Visual Basic 2005 BASICS

yo 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. Microsoft Visual Basic 2005 BASICS

Using Variables (cont.) Use mathematical operators to perform calculations with numeric variables. Output the value in a variable. Assign the value to a label. Microsoft Visual Basic 2005 BASICS

Using Variables (cont.) Microsoft Visual Basic 2005 BASICS

Using Variables (cont.) Microsoft Visual Basic 2005 BASICS

Scope The term “scope” refers to the reach of a variable. General rule yo Scope The term “scope” refers to the reach of a variable. General rule You should declare variables as locally as possible. Microsoft Visual Basic 2005 BASICS

Three Levels of Scope Levels Local variable Form-level variable yo 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 Microsoft Visual Basic 2005 BASICS

The Declarations Section yo The Declarations Section Access the Declarations section Select (Declarations) from the Method Name list that appears at the top of the Code window. Microsoft Visual Basic 2005 BASICS

The Declarations Section (cont.) Microsoft Visual Basic 2005 BASICS

The Declarations Section (cont.) Microsoft Visual Basic 2005 BASICS

Using the Object Data Type yo 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 Microsoft Visual Basic 2005 BASICS

yo 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. Microsoft Visual Basic 2005 BASICS

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. Microsoft Visual Basic 2005 BASICS

yo 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. Microsoft Visual Basic 2005 BASICS

yo 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. Microsoft Visual Basic 2005 BASICS