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Every day we deal with many kinds of data. Examples of data are names, addresses, money, dates, share prices, bills, phone numbers and more. Similarly, in Visual Basic 2010, we have to deal different types of data.
6.1 Visual Basic 2010 Data Types
We classify Visual Basic 2010 data into two major data types, the numeric data types and the non-numeric data types.
6.1.1 Numeric Data Types
Numeric data types are data that consist of numbers that we can calculate them using mathematical operators. In Visual Basic 2010, we categorise numeric data into 7 types, depending on the range of values they can store. Calculations that only involve round figures can use Integer or a Long integer in the computation. On the other hand, high precision calculations need to use Single and Double decision data types, which are also called floating point numbers.
In addition, for currency calculation, you can use the currency data types. Lastly, if even more precision is required to perform calculations that involve many decimal points, we can use the decimal data types. These data types are summarized in Table 6.1.
Table 6.1 Numeric Data
|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
|Variant(numeric)||16 bytes||Any value as large as double|
|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
6.1.2 Non-numeric Data Types
Non-numeric data types are data that cannot be manipulated using standard arithmetic operators. The non-numeric data comprises text or string data types, the Date data types, the Boolean data types( only can store a true or false value), Object data type and Variant data type. We summarise them in Table 6.2.
Table 6.2 Non-numeric Data
|Data Type||Storage||Range of Values|
|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 3,9999|
|Boolean||2 bytes||True or False|
|Object||4 bytes||Any embedded object|
|Varient(text)||Length+22 bytes||Same as variable-length string|
6.1.3 Suffixes for Literals
Literals are values that you assign to a data. In some cases, we need to add a suffix behind a literal so that VB2010 can handle the calculation more accurately. For example, we can use num=1.3089# for a Double type data. Some of the suffixes are displayed in Table 6.3.
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 mailboxes in the post office. The contents of the variables change every now and then, just like the mailboxes. In term of VB2010, variables are areas allocated by the computer memory to hold data. Like the mailboxes, each variable must be given a name. To name a variable in Visual Basic 2010, 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 2010
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
|Valid Name||Invalid Name|
|Long_Name_Can_Be_USED||He&HisFather *& Not allowed|
6.2.2 Declaring Variables
In Visual Basic 2010, 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
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.
Dim yourName as String * 10
yourName can hold 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
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
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 syntax to declare a constant is
Const Constant Name As Data Type = Value
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