Variables are named entities used to store data.
Variables
Variables are used to store data.
The name of a variable must begin with an alphabetic character and
cannot contain whitespace or reserved characters.
A variable can be of a
specific type, indicating the kind of data it stores. String variables store
string values ("Welcome to w3ii"), integer variables store number values
(103), date variables store date values, etc.
Variables are declared
using the Dim keyword, or by using the type (if you want to declare the type),
but ASP.NET can usually determine data types automatically.
Examples
//
Using the Dim keyword:
Dim greeting = "Welcome to w3ii"
Dim counter = 103
Dim today = DateTime.Today
// Using data types:
Dim greeting As String = "Welcome to w3ii"
Dim counter As Integer =
103
Dim today As DateTime = DateTime.Today
Data Types
Below is a list of common data types:
| Type | Description | Examples |
|---|---|---|
| integer | Integer (whole numbers) | 103, 12, 5168 |
| double | 64 bit floating-point number | 3.14, 3.4e38 |
| decimal | Decimal number (higher precision) | 1037.196543 |
| boolean | Boolean | true, false |
| string | String | "Hello w3ii", "John" |
Operators
An operator tells ASP.NET what kind of command to perform in an expression.
The VB language supports many operators. Below is a list of common operators:
| Operator | Description | Example |
|---|---|---|
| = | Assigns a value to a variable. | i=6 |
| + - * / |
Adds a value or variable. Subtracts a value or variable. Multiplies a value or variable. Divides a value or variable. |
i=5+5 i=5-5 i=5*5 i=5/5 |
| += -= |
Increments a variable. Decrements a variable. |
i += 1 i -= 1 |
| = | Equality. Returns true if values are equal. | if i=10 |
| <> | Inequality. Returns true if values are not equal. | if <>10 |
| < > <= >= |
Less than. Greater than. Less than or equal. Greater than or equal. |
if i<10 if i>10 if i<=10 if i>=10 |
| & | Adding strings (concatenation). | "w3" & "schools" |
| . | Dot. Separate objects and methods. | DateTime.Hour |
| () | Parenthesis. Groups values. | (i+5) |
| () | Parenthesis. Passes parameters. | x=Add(i,5) |
| () | Parenthesis. Accesses values in arrays or collections. | name(3) |
| Not | Not. Reverses true or false. | if Not ready |
| And OR |
Logical AND. Logical OR. |
if ready And clear if ready Or clear |
| AndAlso orElse |
Extended Logical AND. Extended Logical OR. |
if ready AndAlso clear if ready OrElse clear |
Converting Data Types
Converting from one data type to another is sometimes useful.
The most
common example is to convert string input to another type, such as an integer or
a date.
As a rule, user input comes as strings, even if the user entered a number. Therefore, numeric input values must be converted to numbers before they can be used in calculations.
Below is a list of common conversion methods:
| Method | Decryptions | Example |
|---|---|---|
| AsInt() IsInt() |
Converts a string to an integer. | if myString.IsInt() then myInt=myString.AsInt() end if |
| AsFloat() IsFloat() |
Converts a string to a floating-point number. | if myString.IsFloat() then myFloat=myString.AsFloat() end if |
| AsDecimal() IsDecimal() |
Converts a string to a decimal number. | if myString.IsDecimal() then myDec=myString.AsDecimal() end if |
| AsDateTime() IsDateTime() |
Converts a string to an ASP.NET DateTime type. | myString="10/10/2012" myDate=myString.AsDateTime() |
| AsBool() IsBool() |
Converts a string to a Boolean. | myString="True" myBool=myString.AsBool() |
| ToString() | Converts any data type to a string. | myInt=1234 myString=myInt.ToString() |