11115_Programming Constructs in VB

7/27/2019 11115_Programming Constructs in VB

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Programming Syntax in VB.NET


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Visual Basic Keywords

Every Programming language uses a set of predefined words. These words

are language-specific and are known as keywords.

Keyword has a specific predefined meaning for the compiler. It is one of

the essential part of a language definition.

Visual Basic provides two types of Keywords such as :-1) Reserved Keywords:- These keywords are those that cannot be used as

names for programming elements, such as variables, methods and classes.

2) Unreserved Keywords:-These keywords can be used as programming

elements, such as variables and procedures.

Examples for Reserved Keywords:-If, Then, Integer, String, Namespace,For, ElseIf, Sub, Long, Double etc

Examples for Unreserved Keywords:- Binary, Preserve, From, IsTrue etc


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Visual Basic Data Types

Data Type Storage Size Value Range

Boolean Depends upon the platform True or False

Byte 1 Byte 0 through 255

Char(single character) 2 Bytes 0 through 65535

Date 8 Bytes 0:00:00 on Jan1,0001 through11:59:59 PM on December

31,9999

Decimal 16 Bytes Very Huge Range

Double 8 Bytes Very Huge Range

Integer 4 Bytes -2147483648 to 2147483647Long 8 bytes Almost 3 times the range of

Integer

String Depends upon Platform Vey Huge Range


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Data Type Conversion

While Working with data types in Visual Basic, there can be a need to

convert variable of one data type into some other data type. So, in that

case we need to use type conversion. While doing conversion we must

ensure that compatibility between two types is there or not.

For achieving this we have various Data type conversion functions such

as:-

CBool

CByte

CChar

CDate

CInt

CStr


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Variables in Visual Basic

A variable is an identifier that denotes a storage area in the memory. This

area can have many values such as:-3,5.2 or Hello World.

We should remember following points while declaring variables in Visual

Basic such as:-

A variable name can only contain Alphabets, digits, and Underscores. A variable name should not begin with a digit or numeric value

A variable name cannot contain a blank space

Keywords cannot be used as variable names

Example for Declaration:-

Dim x As String

Dim Y As Integer

Dim Z As Char


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Constants in VB

We can also assign the values to the variables at the declaration time such

as:-

Dim x As String=Hello

Dim y As Integer=100

Dim Grades As Char=A Constants:- Constants are the name given to the values that do not

change during the execution of a program. It is useful when we have to

use the same value at several places in the program

To declare constant we need to use Const keyword in VB, such as:-

Const Pi=3.14159


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Working with different types of

Operators

Arithmetic Operators

Assignment Operators

Concatenation Operators

Comparison Operators Logical and bitwise Operators


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Operators Description

Arithmetic operators are used to perform arithmetic operations such as

subtraction, multiplication, etc

Example:----+,-,*,/,^,Mod(It will return Remainder)

Assignment operators stores the result of an operation in a variable on

the left side of the operator Example:---- =,*=,+=

Concatenation Operator:-The process of combining two text strings into

one string is called string concatenation.

Example:- &,+

Comparison Operators:-These operators are used to compare two

expressions. We can use these operators to compare numeric values,

strings etc.

Example:-=,,,= etc


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Operators continued..

Logical and Bitwise Operators:-Logical operators are those which are usedwith expressions and produce a Boolean Value.

The Not Operator:-It reverses the logical value of its operand in Boolean valuemeans True to False and False to True.

Example:-

Dim X,Y As BooleanX=Not 5>3(It will return False)

Y=Not 2>7(It will return True)

The And Operator:-It is used to perform logical conjunction of two Booleanexpressions.

Example:-Dim X,Y As Boolean

X=21>14 And 15>9

Y=12>26 And 24>8


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Operators Continued.

The Or operator:-This operator is used to perform a logical operation

between two Boolean expressions. If both the expressions returns false

results then the entire result is false otherwise it will return true.

The Xor Operator:-It performs the logical exclusion on two Boolean

expressions. If only one Boolean expression evaluates to true, then the

final result after applying the Xor operation is true.

Example:-

Dim X,Y As Boolean

X=28>14 Xor 5>9

Y=25>29 Xor14>15


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Operator Precedence

It is a set of rules that specifies the order in which the

operators in Visual Basic are evaluated. In other words,

operator precedence determines which operation is executed

first in an expression involving multiple operators.

According to the rules of precedence, arithmetic and

concatenation operators have higher precedence than the

comparison operators, comparison operators have higher

precedence than logical operators.

The arithmetic operators has highest precedence than all theavailable operators.


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Precedence order

1st Precedence:-Arithmetic Operators in the order such as:- Exponentiation(^)

Unary identity and negation(+,-)

Multiplication and Division(*,/)

Modulus Arithmetic(Mod)

Addition and Subtraction(+,-)

2nd Precedence:-Concatenation Operators +,&

3rd Precedence:-Comparison Operators Equality(=)

Inequality() Less than, greater than()

Greater than or equal to(>=)

Less than or equal to(


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Precedence Order Continued

Lowest Precedence:-Logical Operators

Negation(Not)

Conjunction(And)

Inclusion(Or) Exclusive Disjunction(Xor)


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Selection Statements

Selection Statements are statements that change the flow of a

program based on whether a specific condition is met or not.

Visual Basic supports two types of selection statements:-

The If.Else Statement

The Select..Case Statement

If . Else Statement

This statement is used to test whether a certain condition is

fulfilled or not. If condition is fulfilled, the program control istransferred to the blocks of code inside the ifstatement,

otherwise the program control is transferred to another block

of statement.


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If-Else Continued..

Syntax in VBIf condition [Then]

[statements]

[ElseIf elseifcondition [Then] ]

[Else

[elsestatements] ]End If

Example No. 1:-

Dim x As Integer

x = CInt(TextBox1.Text())

If x Mod 2 = 0 Then

MessageBox.Show(x & "is Even")

Else

MessageBox.Show(x & "is Odd")

End If


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Examples Continued.

Example No.2:-If-else,elseifDim x1 As String

x1 = TextBox1.Text

If x1 = "hello" Then

MessageBox.Show(TextBox1.Text)ElseIf x1 = "bye" Then

MessageBox.Show(TextBox1.Text)

ElseIf x1 = "lpu" Then

MessageBox.Show(TextBox1.Text)

ElseMessageBox.Show("You have Entered something else")

End If


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Iteration Statements

An Iteration Statement executes a statement or set of

statements repeatedly. Visual Basic supports four types of

Iteration Statements:-

The While..End While Statement

The Do.Loop Statement

The For.Next Statement

The For EachNext Statement


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Using WhileEnd While Statement

It continues to execute a set of statements as long as a givencondition is true.

Syntax:-

While condition

[Statements]

End While

Example:-

Dim x = 1

While x


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DoWhile/Until Loop Statement

It also executes a group of statements repeatedly. But as it is alreadyknown that Do loop will work for at least one time even if the condition isnot true. So it will also work accordingly.

Syntax:-

Do

[Statements]Loop while [condition]

Example:-

Dim x = 12

Do

ListBox1.Items.Add(x)

Loop While x


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Do-Until Loop

As Do-While Works until condition is true and when the condition is false

it will terminate, but we also have Do-Until loop which works until the

condition is false. When the condition becomes true it will get terminated.

Syntax:-

Do[Statements]

Loop Until [condition]

Example:-

Dim X As String

Do

X = InputBox("Correct Password Please")

Loop Until X = "Ranger"


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For.Next Statement

The ForNext statement is used when you have to execute a group a

statements repeatedly for a specified number of times.

Syntax:-

For counter [As datatype]=start to end [step step]

[statements]Next [counter]

Example 1:-

For i As Integer = 8 To 1 Step -2

ListBox1.Items.Add(i)

Next i


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For..Next Statement Continued..

Example 2:-


If i = 4 Then

Continue For

End If


Next I

Example 3:-


If i = 2 Then

Exit For

End If


Next i


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For Each..Next Statement

For Each.Next statement iterates through all the items in alist which may be an array or collection of objects. Thisstatement works in the same way as the ForNext statement.

The Benefit of using For Each..Next statement is that we

dont need to pass the starting and ending limits. It will iteratethrough the collection/list automatically.

Syntax:-

For Each element [As datatype] in group

[Statements]

[Exit For]

[Statements[

Next [element]


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For Each Next Continued

Example1:-

Dim num As Integer() = {30, 40, 50, 60, 70}

For Each i As Integer In num


Next

Example 2:-



If i = 40 Then

Continue ForEnd If


Next


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For EachNext Continued

Example 3:-



If i = 40 Then

Exit ForEnd If


Next

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11115_Programming Constructs in VB