Data types and variables lesson 6
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Data Types and Variables Lesson 6!. 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 Type Range Whole Number: Integer-32,768 to 32,767 Long-2,147,483,648 to 2,147,483,647

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Data Types and Variables Lesson 6!

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Data types and variables lesson 6

Data Types and VariablesLesson 6!


Data type

Data Type!

Computers are all about Data!

Data can be in the form of

  • Text

  • Dates

  • Sounds

  • Pictures


Data types and variables lesson 6

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-1,79769313486232E+308

to 1,79769313486232E+308


Data types and variables lesson 6

Data TypeRange

Other Types:

String1 to about 65,000

characters

DateJanuary 1, 100 to

December 31, 9999

BooleanTrue or False


Variable

Variable!

Definition:

Memory locations where temporary data is stored.


Facts about variables

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

Declaring Variables

  • The first step to using a variable in your program is to:

    • 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.

  • The above process is called declaring a variable!


Example

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

Rules for Naming Variables!

When naming variables, keep the following rules in mind.

  • Variable names must begin with an alphabetic character ( a letter).

  • Following the first character, letters, numbers, and the underscore (_) are allowed.

  • Variable names cannot include any spaces.

  • Variable names can be up to 255 character long.


Using the prefix rule

Using the Prefix Rule!

PrefixData TypeExample

intIntegerintPeople

lngLonglngInches

sngSinglesngWeight

dblDoubledblMass

strStringstrName

dteDatedteAnniversary

blnBooleanblnSold


Data types and variables lesson 6

Example Program:

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


Data types and variables lesson 6

  • 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


Data types and variables lesson 6

  • 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.


Data types and variables lesson 6

  • 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


Data types and variables lesson 6

  • 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.


Data types and variables lesson 6

  • 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


Data types and variables lesson 6

  • 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

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.


Summary1

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 (=).


Data types and variables lesson 6

Homework:

Pick up a worksheet before

you leave!


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