Visual Basic 2008 Tutorial
Lesson 6: Managing VB2008 Data




There are many types of data that we come across in our daily life. For example, we need to handle data such as names, addresses, money, date, stock quotes, statistics and etc everyday. Similarly in Visual Basic 2008, we have to deal with all sorts of of data, some can be mathematically calculated while some are in the form of text or other forms. VB2008 divides data into different types so that it is easier to manage when we need to write the code involving those data.
6.1 Visual Basic 2008 Data Types

Visual Basic 2008 classifies the information mentioned above into two major data types, they are the numeric data types and the non-numeric data types.

6.1.1 Numeric Data Types


Numeric data types are types of data that consist of numbers, which can be computed mathematically with various standard operators such as add, minus, multiply, divide and so on. Examples of numeric data types are your examination marks, your height, your weight, the number of students in a class, share values, price of goods, monthly bills, fees and etc. In Visual Basic 2008, numeric data are divided into 7 types, depending on the range of values they can store. Calculations that only involve round figures or data that don't need precision can use Integer or Long integer in the computation. Programs that require high precision calculation need to use Single and Double decision data types, they are also called floating point numbers. For currency calculation , you can use the currency data types. Lastly, if even more precision is requires to perform calculations that involve a many decimal points, we can use the decimal data types. These data types summarized in Table 6.1


Table 6.1: Numeric Data Types

Type
Storage
Range of Values

Byte
1 byte
0 to 255

Integer
2 bytes
-32,768 to 32,767

Long
4 bytes
-2,147,483,648 to 2,147,483,648

Single
4 bytes
-3.402823E+38 to -1.401298E-45 for negative values
1.401298E-45 to 3.402823E+38 for positive values.

Double
8 bytes
-1.79769313486232e+308 to -4.94065645841247E-324 for negative values
4.94065645841247E-324 to 1.79769313486232e+308 for positive values.

Currency
8 bytes
-922,337,203,685,477.5808 to 922,337,203,685,477.5807

Decimal
12 bytes
+/- 79,228,162,514,264,337,593,543,950,335 if no decimal is use
+/- 7.9228162514264337593543950335 (28 decimal places).


¡¡


¡¡


6.1.2 Non-numeric Data Types

Nonnumeric data types are data that cannot be manipulated mathematically using standard arithmetic operators. The non-numeric data comprises text or string data types, the Date data types, the Boolean data types that store only two values (true or false), Object data type and Variant data type .They are summarized in Table 6.2




Table 6.2: Nonnumeric Data Types

Data Type
Storage
Range

String(fixed length)
Length of string
1 to 65,400 characters

String(variable length)
Length + 10 bytes
0 to 2 billion characters

Date
8 bytes
January 1, 100 to December 31, 9999

Boolean
2 bytes
True or False

Object
4 bytes
Any embedded object

Variant(numeric)
16 bytes
Any value as large as Double

Variant(text)
Length+22 bytes
Same as variable-length string



In addition, we need to enclose string literals within two quotations and date and time literals within two # sign. Strings can contain any characters, including numbers. The following are few examples:

memberName="Turban, John."
TelNumber="1800-900-888-777"
LastDay=#31-Dec-00#
ExpTime=#12:00 am#

¡¡

6.2 Managing Variables

Variables are like mail boxes in the post office. The contents of the variables changes every now and then, just like the mail boxes. In term of VB2008, variables are areas allocated by the computer memory to hold data. Like the mail boxes, each variable must be given a name. To name a variable in Visual Basic 2008, you have to follow a set of rules.

6.2.1 Variable Names

The following are the rules when naming the variables in Visual Basic 2008

It must be less than 255 characters
No spacing is allowed
It must not begin with a number
Period is not permitted
Examples of valid and invalid variable names are displayed in Table 6.4

Table 6.4

Valid Name
Invalid Name

My_Car
My.Car

ThisYear
1NewBoy

Long_Name_Can_beUSE
He&HisFather *& is not acceptable


6.2.2 Declaring Variables

In Visual Basic 2008, one needs to declare the variables before using them by assigning names and data types. If you fail to do so, the program will show an error. They are normally declared in the general section of the codes' windows using the Dim statement.
The format is as follows:

Dim Variable Name As Data Type

Example 6.1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load


Dim password As String
Dim yourName As String
Dim firstnum As Integer
Dim secondnum As Integer
Dim total As Integer
Dim doDate As Date

End Sub

You may also combine them in one line , separating each variable with a comma, as follows:

Dim password As String, yourName As String, firstnum As Integer,.............

For string declaration, there are two possible formats, one for the variable-length string and another for the fixed-length string. For the variable-length string, just use the same format as example 6.1 above. However, for the fixed-length string, you have to use the format as shown below:

Dim VariableName as String * n, where n defines the number of characters the string can hold.

Example 6.2:

Dim yourName as String * 10

yourName can holds no more than 10 Characters.

6.2.3 Assigning Values to Variables

After declaring various variables using the Dim statements, we can assign values to those variables. The general format of an assignment is

Variable=Expression

The variable can be a declared variable or a control property value. The expression could be a mathematical expression, a number, a string, a Boolean value (true or false) and etc. The following are some examples:

firstNumber=100
secondNumber=firstNumber-99
userName="John Lyan"
userpass.Text = password
Label1.Visible = True
Command1.Visible = false
Label4.Caption = textbox1.Text
ThirdNumber = Val(usernum1.Text)
total = firstNumber + secondNumber+ThirdNumber

6.3 Constants

Constants are different from variables in the sense that their values do not change during the running of the program.

6.3.1 Declaring a Constant

The format to declare a constant is

Const Constant Name As Data Type = Value

Example 6.3

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Const Pi As Single=3.142

Const Temp As Single=37

Const Score As Single=100

End Sub





source : http://www.vbtutor.net/vb2008/vb2008tutor.html


--------------------------------------------------------


Dokter PC

Trik Domain Gratis

Trik Download game free

Trik Download Video

Broadband-internet

Trik Buat Antivirus

Trik-download-dari-google

Trik Cara Melacak IP

Trik Choose Phone

Trik woodwork-stores