Fundamentals of .Net Programming concepts

Fundamentals
of
VB.Net
Dr.A.Bharathi Lakshmi,
Head and Assistant Professor of IT,
V.V.Vanniaperumal College for Women,
Virudhunagar.

Variables & Constants
 Variables
• Container that stores one or more values
• Name of the variable is unchanged.
• The value might change during execution.
 Constants
• Stores a constant value
• Name as well as the value cannot be changed during
execution.

Data Types
Data Types Description
Integer 32-bit number – numeric data
Long 64-bit number – numeric data
Short 16-bit number – numeric data
Byte ASCII characters value in a numeric format – binary data
Double Huge floating point numbers
Single Single precision floating point numbers
Decimal Very large floating point numbers
Boolean 16-bit number – Boolean values
Char Single character
DateTime Date and time information
String Alphanumeric data
Object Data of any type

Rules for Naming variables
 It must begin with a letter
 It cannot contain a period or an
identifier-type character
 It must not exceed 255 characters
 It must be unique within the scope.

Declaring Variables
 Dim statement is used to declare a
variable
Syntax
Dim VariableName [As type]
VariableName – name of the variable
type – data type
Declaration
Dim ivar
Dim svar=“Hello”
Dim ivar1,ivar2 as integer
Initialization
Dim ivar as Integer
ivar=25

New Keyword
 New keyword initialize the variables before using
them in the code
Examples
Dim Inta as Object
Inta= new Integer
dim Ints as new Integer()

Nothing Keyword
 Represents default value of any data type
 Re-initialize to its default value.
Examples
Dim Inta as Integer=20
Inta= inta+4
Inta=Nothing

Explicit declaration
 Can be declared implicitly as well as
explicitly
 Without declaring a variable ,if it is
used it is implicitly declared
Example
InCo=20*5
Option Explicit [on|off]
 On – explicit declaration
 Off – implicit declaration
 Default - on

Scope of a variables
 Defines it visiblity
 The part of the program that can
access the variable
 Based on scope, variables can be
divided into two types
• Procedure-level variables
• Module-level variables

Procedure-Level Variables
 Only accessed within the procedure
 Reffered as local variables
Sub MyPro()
Dim str as String
str=“Hello “
MsgBox(str)
End Sub
In this code the variable str can be used only within the
procedure MyPro()

Module-Level Variables
 Declared in the declaration section of the
Module.
 Module level variables are classified into
• Private – can be used within the modules
Private str as String
Sub MyPro()
str=“Hello “
End Sub
Sub display()
MsgBox(str)
End Sub
• Public – can be used across modules
Public str as String
Sub MyPro()
str=“Hello “
End Sub
Sub display()
MsgBox(str)

Declaring Constants
 Const Keyword is used to declare a
constant
Syntax
Const ConstantName [As type]
ConstantName – name of the constant
type – data type
Example
Const cd as integer =25
Dim ivar as Integer
if ivar =1000 then
MessageBox.show(“Discount offered is “ & cd &
“%”)
End if

Operators
 Perform actions on data.
 Actions can be classified as
• Mathematical Calculations
• Assigning values to variables
• Comparing data
• Binary calculations
Example
a=15+30
(+) sign is the mathematical operator
the added value will be stored in a using
assignment operator

Types of Operators
 Arithmetic
 Comparison
 Logical/bitwise

Arithmetic Operators
 Performs Mathematical calculations.
 The arithmetic Operators are
• + operator – Add two numebers
• - operator – Subtract two numbers
• * operator – Multiply two numbers
• / operator – divide two numbers returns
floating
point number
• operator – divide two numbers returns
Integer
point number
• ^ operator – power for a specified number
x^y

Comparison Operators
 Used to compare the expression
 The operators are
• Relational Operators
 Compares two numerical values
 <.>,<=,>=,<> and =
 Returns a Boolean value
• Is Operators
 Compares two object references
 Check if they are identical
• Like Operators
 Compares two strings
 Case sensitive

Logical/Bitwise Operators
 Perform logical Operations
 Logical operators are
• And operator
• Or operator
• Not operator
• Xor operator
• AndAlso operator
• OrElse operator

 And operator
• Performs AND logical operations
• Returns true only when all expressions return true.
Example
Dim res as Boolean
Dim x as Integer = 40
Dim y as Integer = 30
Dim z as Integer = 20
res=x>y and y>z ‘Returns true
res=y>x and y>z ‘Returns false

 Or operator
• Performs OR logical operations
• Returns true if any one of the expressions
return true.
Example
Dim res as Boolean
res=x>y Or y>z ‘Returns true
res=y>x Or y>z ‘Returns true

 Not operator
• Performs NOT logical operations.
• Negates the value of expression and returns the opposite
value.
• If true result will be false and vise versa.
Example
Dim res as Boolean
res=Not(x>y) ‘Returns False
res=Not(y>x) ‘Returns True

 Xor operator
• Performs XOR logical operations
• Performs logical exclusion on two
expressions.
• Returns true if any one of the expression
returns true value
• Returns false if all the expression returns
same value
Example
Dim res as Boolean
res=x>y Xor y>z ‘Returns false
res=y>x Xor y>z ‘Returns true

 AndAlso operator
• Performs AND logical operations
• If first expression returns false then the second expression
wont be evaluated
Example
Dim res as Boolean
res=x>y AndAlso y>z ‘Returns true
res=y>x AndAlso y>z ‘Returns false

 OrElse Operator
• Performs OR logical operations
• If first expression returns true then the second expression
wont be evaluated.
Example
Dim res as Boolean
res=x>y OrElse y>z ‘Returns true
res=y>x OrElse y>z ‘Returns true

Operator Precedence
 Order of evaluation of expressions
 Order of precedence
• Arithmetic Operators
 ^
 * & /

 + & -
• Comparison Operators
 =
 <>
 < & >
 >=
 <=
 Like
 Is
• Logical/Bitwise Operators
 Not
 And & AndAlso
 Or & OrElse

Operator Precedence
Example
2+3*4+5
a)20 b)45 c) 17 d) none
7-8+5
a) 6 b) -5 c) -4 d) 4

Expressions
 Combination of operators and operands.
 The value of the expressions are calculated at the
time of execution.
 Three types of expressions
• Numeric
• Value Comparison
• Boolean

Expressions
 Numeric Expressions
• Returns numeric values
• Is calculated using operator precedence rules
Examples
Dim cel as Integer
Dim far as Integer = 90
cal= (5/9)* (far-32)

Expressions
 Value comparison expressions
• Compare values
• Comparison operators are used
Examples
if x>250 then
MessageBox.Show(“>250”)
else
MessageBox.Show(“<=250”)
end if

Expressions
 Boolean Expressions
• Evaluates a Boolean value
Examples
if pass=true then
MessageBox.Show(“pass”)
else
MessageBox.Show(“fail”)
end if

Conversions
 Assigns the value of a variable of a data type to a
variable of another data type.
 If the value of the integer variable is assign to a long
variable it is broadening
 If the value of the long variable is assign to an integer
variable it is narrowing
 Types
• Implicit – broadening
• Explicit – narrowing (type.parse())

Controlling Program Flow
• Decision statements
 Execute stmts. based on the condition
 If…Then
 If…Then…Else
 Select…Case
• Looping Statement
 While…End While
 Do…Loop
 For…Next
 For…Each…Next

Decision Statements
 If…Then
• To execute a block of code based on a certain
condition
Syntax
If <<condition>> Then
‘Statements to be executed
End If

Decision Statements
 If…Then…Else
• Same as If…Then
• Two blocks of code can be executed for true case as
well as for false case
Syntax
If <<condition>> Then
‘Execute Statements if condition is true
Else
‘Execute Statements if condition is false
End If

Decision Statements
 Select…Case Statement
• Execute a group of statements based on the
test expression
• Can be a single variable or complex
expression
Syntax
Select <<testvalue>>
‘Execute a set of statements
Case <<value1>>
Case <<value2>>
Case <<value3>>
Case Else
End Select

Looping Statements
 While…End While
• Set of statements will be executed until the condition
becomes false.
Syntax
While <<condition>>
‘Executes statements
End While

Looping Statements
 Do…Loop
• Same as while loop
• Executes the block of code first without evaluating the
condition
• Then the condition is evaluated
Syntax
do
Loop While <<condition>>

Looping Statements
 For…Next Statement
• Same as while…end while
• Block of code will be executed for a fixed number of
times.
Syntax
For <<varnam>>=<<start>> to <<end>> Step <<value>>
Next

Looping Statements
 For…Each…Next Statement
• Similar to For...Next statement
• Enables to traverse through a collection
such as an array or a row of a table.
Syntax
For each <<varnam>> In <<array name or collection>>
Next
Examples
Dim I as integer
For Each I in Arrnam
Console.WriteLine(arrnam(i))
Next

Fundamentals of .Net Programming concepts

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