Variable and constants in Vb.NET

VB.NET:- Variable and Constants
BCA -501

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Content
 Variable
 Variable Declarations
 Variable Declaration Example
 Variable Initialisations
 Getting Values from user
 Lvalues & Rvalues
 Constants
 Enumeration
 Scope of Variable

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Variable
 A variable is used to hold the value that can be used further in the programming.
 A variable is a simple name used to store the value of a specific data type in computer memory.
 In VB.NET, each variable has a particular data type that determines the size, range, and fixed
space in computer memory.
 With the help of variable, we can perform several operations and manipulate data values in any
programming language.

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Variable Declarations
The Dim statement is used for variable declaration and storage allocation for one or more
variables. The Dim statement is used at module, class, structure, procedure or block level. .
Each variable in the variable list has the following syntax and parts −
variablename[ ( [ boundslist ] ) ] [ As [ New ] datatype ] [ = initializer ]
Where,
 variablename − is the name of the variable
 boundslist − optional. It provides list of bounds of each dimension of an array variable.
 New − optional. It creates a new instance of the class when the Dim statement runs.
 datatype − Required if Option Strict is On. It specifies the data type of the variable.
 initializer − Optional if New is not specified. Expression that is evaluated and assigned to the
variable when it is created.

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Variable Declarations Syntax
Syntax: Dim [Variable_Name] As [Defined Data Type]
Name Descriptions
Dim It is used to declare and allocate the space for one or more variables in memory.
Variable_Name It defines the name of the variable to store the values.
As It is a keyword that allows you to define the data type in the declaration statement.
Data Type It defines a data type that allows variables to store data types such as Char, String, Integer,
Decimal, Long, etc.
Value Assign a value to the variable.

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Variable Declarations Example
Dim Roll_no As Integer
Dim Emp_name As String
Dim Salary As Double
Dim Emp_id, Stud_id As Integer
Dim result_status As Boolean
Note:
If we want to declare more than one variable in the same line, we must separate each variable with a comma.
Dim Variable_name1 As DataType1, variable_name2 As DataType2, Variable_name3 As DataType3

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Variable Initialization
 After the declaration of a variable, we must assign a value to the variable. The following syntax
describes the initialization of a variable:
Syntax: Variable_name = value
Dim Roll_no As Integer 'declaration of Roll_no
Roll_no = 101 'initialization of Roll_no
Initialize the Emp_name
Dim Emp_name As String
Emp_name = “Jaya" 'Here Emp_name variable assigned a value of Jaya
Initialize a Boolean variable
Dim status As Boolean 'Boolean value can be True or False.
status = True 'Initialize status value to True
Initialzation at the time of declaration:
Dim Roll_no As Integer = 101
Dim Emp_name As String = " Stephen Robert "

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Getting Values from the User:
 In VB.NET, the Console class provides the Readline() function in the System namespace.
 It is used to take input from the user and assign a value to a variable
Dim name As String
name = Console.ReadLine()
Or name = Console.ReadLine
Imports System
Module User_Data
Sub Main()
Dim num As Integer
Dim age As Double
Dim name As String
Console.WriteLine("Enter your favourite number")
' Console.ReadLine or Console.ReadLine() takes value from the user
num = Console.ReadLine
Console.WriteLine(" Enter Your Good name")
'Read string data from the user
name = Console.ReadLine
Console.WriteLine(" Enter your Age")
age = Console.ReadLine
Console.WriteLine(" You have entered {0}", num)
Console.WriteLine(" You have entered {0}", name)
Console.WriteLine(" You have entered {0}", age)
Console.ReadKey()
End Sub
End Module
Note: Console.Read() and
Console.ReadKey() function is
used to read a single character
from the user.

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Lvalues & Rvalues
 Lvalue: It is an lvalue expression that refers to a memory location for storing the address of a
variable. An lvalue is a variable that can appear to the left or right of the assignment operator to
hold values. Furthermore, in comparison to or swapping the variables' values, we can also
define the variable on both sides (left or right-side) of the assignment operator.
Dim num As Integer
Num = 5
Or
Dim num As Integer = 5
But when we write the following statement, it generates a compile-time error because it is not a
valid statement.
Dim x As Integer
10 = x
 Rvalue: It is an rvalue expression that is used to store a value in some address of memory. An
rvalue can appear only on the right- hand side because it is a value of the variable that defines
on the right-hand side.
Dim college_name As String
college_name = “ISM" // rvalue define at right side of the assignment operator.

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Constants in VB.NET
 The name constant refers to a fixed value that cannot be changed during the execution of a program.
 It is also known as literals.
 These constants can be of any data type, such as Integer, Double, String, Decimal, Single, character, enum,
etc.
 In VB.NET, const is a keyword that is used to declare a variable as constant. The Const statement can be
used with module, structure, procedure, form, and class.
Const constname As datatype = value
Item Name Descriptions
Const It is a Const keyword to declare a variable as constant.
Constname It defines the name of the constant variable to store the values.
As It is a keyword that allows you to define the data type in the declaration statement.
Data Type It defines a data type that allows variables to store data types such as Char, String,
Integer, Decimal, Long, etc.
Value Assign a value to the variable as constant.

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Print and Display Constant
Const Name Descriptions
vbCrLf Carriage return/linefeed character combination
vbCr Carriage return character
vbLf Linefeed character
vbNewLine Newline character
vbNullChar Null character
vbNullString Not the same as a zero-length string (""); used for calling external procedures.
vbObjectError Error number. User-defined error numbers should be greater than this value. For example:
Err.Raise(Number) = vbObjectError + 1000
vbTab Tab character.
vbBack Backspace character.

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Enumerations in VB.NET
 An enumerated type is declared using the Enum statement.
 The Enum statement declares an enumeration and defines the values of its members.
 The Enum statement can be used at the module, class, structure, procedure, or block level.
Each member in the memberlist has the following syntax and
parts:
[< attribute list >] member name [ = initializer ]
Where,
name − specifies the name of the member. Required.
initializer − value assigned to the enumeration member. Optional.
Example:
Enum Colors
red = 1
orange = 2
yellow = 3
green = 4
azure = 5
blue = 6
violet = 7
End Enum

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Print and Display Constant
Const Name Descriptions
vbCrLf Carriage return/linefeed character combination
vbCr Carriage return character
vbLf Linefeed character
vbNewLine Newline character
vbNullChar Null character
vbNullString Not the same as a zero-length string (""); used for calling external procedures.
vbObjectError Error number. User-defined error numbers should be greater than this value. For example:
Err.Raise(Number) = vbObjectError + 1000
vbTab Tab character.
vbBack Backspace character.

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Scope of Variables
The scope of a variable determines the accessible range of a defined variable at the time of
declaration in any block, module, and class.
It can be accessed, if the variable is in a particular region or scope in the same block. And if the
variable goes beyond the region, its scope expires.
The following are the methods to represent the scope of a variable in VB.NET.
1. Procedure Scope
2. Module Scope
3. Public Scope

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Procedure Scope
 A local variable is a type of variable defined within a procedure scope, block, or function. It is
available with a code inside the procedure, and it can be declared using the Dim or
static statement.
 These variables are not accessible from outside of the local method. However, the local
variable can be easily accessed by the nested programming function in the same method.
Dim X As Integer
 Local variables exist until the procedure in which they are declared is executed. Once a
procedure is executed, the values of its local variables will be lost, and the resources used by
these variables will be released. And when the block is executed again, all the local variables
are rearranged.

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Module Scope
 All existing procedures can easily identify a variable that is declared inside a module sheet is
called a module-level variable.
 The defined module variable is visible to all procedures within that module only, but it is not
available for other module's procedures.
 The Dim or private statement at the top of the first procedure declaration can be declared the
module-level variables. It means that these variables cannot be declared inside any procedure
block.
 Further, these variables are useful to share information between the procedures in the same
module.
 And one more thing about the module-level variable is that these variables can remains
existence as long as the module is executed.

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Global Scope
 As the name defines, a global variable is a variable that is used to access the
variables globally in a program.
 It means these variables can be accessed by all the procedures or modules available in a
program.
 To access the variables globally in a program, we need to use the friend or public
keyword with a variable in a module or class at the top of the first procedure function.
 Global scope is also known as the Namespace scope.
'Global declaration of a variable
Public str As String = "Hello, Programmer."
Public topic As String
Public exp As Integer

Variable and constants in Vb.NET

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