Data Types and Variables

Data Type! Computers are all about Data! Data can be in the form of Text Dates Sounds Pictures

Visual Basic supports the following data types: Data TypeRange Whole Number: Integer-32,768 to 32,767 Long-2,147,483,648 to 2,147,483,647 Decimal Number: Single-3,402823E+38 to 3,402823E+38 Double-1, E+308 to 1, E+308

Data TypeRange Other Types: String1 to about 65,000 characters DateJanuary 1, 100 to December 31, 9999 BooleanTrue or False

Variable! Definition: Memory locations where temporary data is stored.

Facts about Variables. Variables are a common feature of programming languages. Variables can be used to store and manipulate all kinds of data. Variables get their name from the fact that the value can vary as the program runs. You can assign values to variables using the assignment operator. (=) You should declare variables before you use them.

Declaring Variables The first step to using a variable in your program is to: 1. Let the compiler know that you want to set up a memory location as a variable. 2. What you want to call the variable. 3. What data type you want the variable to have. The above process is called declaring a variable!

Example: To declare a variable, use the Dim statement as show below. Dim VariableName As DataType The following declare a variable named intAnswer with the Integer data type. Dim intAnswer As Integer

Rules for Naming Variables! When naming variables, keep the following rules in mind. 1. Variable names must begin with an alphabetic character ( a letter). 2. Following the first character, letters, numbers, and the underscore (_) are allowed. 3. Variable names cannot include any spaces. 4. Variable names can be up to 255 character long.

Using the Prefix Rule! PrefixData TypeExample intIntegerintPeople lngLonglngInches sngSinglesngWeight dblDoubledblMass strStringstrName dteDatedteAnniversary blnBooleanblnSold

Example Program: Open VB and create a new form the looks like the following:

Add 5 labels. Set the name properties to the following: Label1 should be lblAgeYears Label2 should be lblMonths Label3 should be lblYou Label4 should be lblOutputMonths Label5 should be lblAgeMonths

Set the Name property of the form to frmMonths and the caption to Month Converter. Set the captions of the five labels to: Age in years: Months since last birthday You are X months old.

Add two text boxes to your form. Set the name of the text boxes to txtYears txtMonths Add one command button. Set the name of the command button to cmdMonths Set the caption to Calculate age in months

Change the properties of the following labels to false. lblYou, lblOutputMonths, lblAgemonths Double-click the Calculate age in months button. Key Dim intMonths As Integer at the top of the event procedure and press the Enter key twice.

Enter the following: 'Calculate Months intMonths = (Val(txtYears.Text) * 12) + _ Val(txtMonths.Text) 'Display Number of Months Old lblOutputMonths.Caption = intMonths lblYou.Visible = True lblOutputMonths.Visible = True lblAgemonths.Visible = True

Run and fix your errors. Enter 5 in the Age in years text box. Enter 4 in the Months since last birthday text box. Click the Calculate age in months button. What is your output?

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.

Summary 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 also a good idea to use naming prefixes to identify the data type of the variable. You should declare variables before you use them. You can assign values to variables using the assignment operator (=).

Homework: Answer the following questions: 1. What is the DIM statement used for? 2. What are the two common integer data types? 3. What are the two common decimal data types? 4. Write Visual Basic code to declare a String variable called strFirstName.