Chapter 3. Elements of VB Programming

Chapter 3. Elements of VB Programming

Data types

Data types are used to store and identify the type of data that are supplied through the variables to a program.

They are, String, Integer, Long, Single, Double, Currency, Date, Boolean and Variant.

Data type/ Key words	Usage	Storage size	Range
String	To store Group of characters enclosed  in double quotes called string	10 bytes + string length	0-2billion
Integer	To represent numeric data without fractions (Whole numbers)	2 bytes	-32768 - +32767
Long	To represent large numeric data without fractions (large Whole numbers)	4 bytes	214 crore (Aprx)
Single	To represent numeric data with fractions (Single precision floating point numbers)	4 bytes	(7 digit Fractional part)
Double	To represent large numeric data with fractions (Double precision floating point numbers)	8 bytes	(16 digits Fractional part)
Currency	To represent financial data	8 bytes	(4 digits Fractional part)
Date	To store date and time in a format	8 bytes
Boolean	For logic variables to store true or false	2 bytes
Variant	It can contain any type of data	22 bytes + string length

Variables

They are named storage locations to hold data. At run time we can change the content of a variable.

Declaring variables

Syntax

Dim Variablename As Datatype

Eg: -

Dim amount As currency

Dim mark As integer

Dim name As string

Variable naming rules

It must be unique not a key word.

It can contain maximum 255 characters.

It must begin with an alphabet.

Symbols, Special symbols, space are not allowed except underscore.

Constants

They are values stored in a variable. They are numeric constants and string constant.

Numeric constants may be integer, long, single, double.

Eg:-   Dim age As Integer

          Age=20

String constants enclosed in double quotes.

Eg: -  Dim state As String

          state= “Kerala”

Operators

          They are symbols used in an expression or operation. Data stored in a variable or constants are processed by using operators.

          They are Arithmetic Operators, Relational Operators, Logical Operators, and Concatenation Operator.

Arithmetic Operators

Operator	Usage	Example A=5, B=2
+	Addition	A+B  (7)
-	Subtraction	A-B (3)
* (Asterisk)	Multiplication	A*B (10)
/	Division	A/B (2.5)
\	Integer Division	A\B (2)
Mod	Reminder of division	A mod B (1)
^ (Cap)	Exponentiation	A ^ B (25)

Relational Operators

They are used to check some conditions. Its result is either true or false. They are

Operator	Usage	Example (A=6, B=9)
=	Equal to	A=B (False)
<	Less than	A<B (True)
>	Greater than	A>B (False)
<=	Less than or equal to	A<=B (True)
>=	Greater than or equal to	A>=B (False)
<>	Not equal to	A<>B (True)

Logical Operators

          It helps us to combine two relational operations. Its output is also true or false. They are AND, OR, NOT

If A and B are outputs of any relational operations, then

A	B	A AND B	A OR B	NOT A	NOT B
T	T	T	T	F	F
T	F	F	T	F	T
F	T	F	T	T	F
F	F	F	F	T	T

Concatenation Operator

It is used to join two strings.

Eg:-

Dim a, b, c as string

a= “Together”

b= “to win”

c= a&b

Its output is: Together to win.

Control Structures

          They are used to alter the normal/ sequential execution of a program. They are classified into two, Decision statements and Loop statements.

Decision statements

It contains an expression (Relational or Logical) it evaluates the condition first and executes a group of statements according to that condition. They are

·        If…..then….

·        If….Then….else….

·        If…..then….Else if….else….

·        Select case

If…then…

Syntax:

If <condition> then

<Statements>

End if

Eg:-

If a>b then

Msgbox “a is large”

Here the condition evaluates first, if it is true the statements will be executed otherwise exit from if statement.

If….Then….else….

Syntax:

If <condition> then

<Statement1>

Else

<statement2>

End if

Eg:-

If a>b then

Msgbox “a is large”

Else

Msgbox “b is large”

End if

Here the condition evaluates first, if it is true the statement1 will be executed otherwise statement2 will be executed.

If…..then….Else if….else….

Syntax

If <condition1> then

<statement1>

elseif <condition2>

<statement2>

elseif <condition3>

<statement3>

…………….

…………….

……………

else

<statements>

end if

Eg:-

If percent > 90 Then

Text3.Text = "A+"

ElseIf percent > 80 AND percent < 90 Then

Text3.Text = "A"

ElseIf percent > 70 AND percent < 80 Then

Text3.Text = "B+"

ElseIf percent > 60 AND percent < 70 Then

Text3.Text = "B"

ElseIf percent > 50 AND percent < 60 Then

Text3.Text = "C+"

ElseIf percent > 40 AND percent < 50 Then

Text3.Text = "C"

ElseIf percent > 30 AND percent < 40 Then

Text3.Text = "D+"

Else

Text3.Text = "D"

End if

          It will display the grade according to the percentage. Here we can include any number of conditions and it works with its true or false results.

Select case statement

The select case statement is used to check different values for an expression.

Syntax

Select case <Expression>

Case <value1>

<statement1>

Case <value2>

<statement2>

Case <value3>

<statement3>

………………

……………..

case else

<statements>

End select

Eg:-

Private Sub Command1_Click()

numday = Text1.Text

Select Case numday

Case 1

MsgBox "Sunday"

Case 2

MsgBox "Monday"

Case 3

MsgBox "Tuesday"

Case 4

MsgBox "Wednesday"

Case 5

MsgBox "Thursday"

Case 6

MsgBox "Friday"

Case 7

MsgBox "Saturday"

Case Else

MsgBox "Enter a valid number of day"

End Select

End Sub

It display the day in a week if the input is 1 to 7 otherwise displays a message box with message "Enter a valid number of day".

Loop statements

Loop statements are used to execute a group of statements repeatedly.

In a loop there is three elements first one is an initialization of loop control variable (To control the repeated execution of statements), second one is the condition checking of loop control variable, third one is updating of loop control variable and last one is loop body (Group of statements that are to be executed repeatedly).

Loop statements are classified as follows,

·        Do…loop (Do while….loop, Do until……loop)

·        While….wend

·        For…..next

Do….loop

Syntax

<Initialization expression>

Do while <Condition expression >

<Body of loop>

<Updating expression >

Loop

Eg:-

Private Sub Command1_Click()

i = 1

Do While i <= 10

Print i

i = i + 1

Loop

End Sub

It will print 1 to 10 on the form. Here Body of loop will executed repeatedly if the condition is true until it false.

Do until………..loop

Syntax

<Initialization expression>

Do until <Condition expression >

<Body of loop>

<Updating expression >

Loop

Eg:-

Private Sub Command1_Click()

i = 1

Do Until i > 10

Print i

i = i + 1

Loop

End Sub

It will print 1 to 10 on the form. Here Body of loop will executed repeatedly if the condition is false until it true.

While…….wend

Syntax

<Initialization expression>

While <Condition expression >

<Body of loop>

<Updating expression >

Wend

Eg:-

Private Sub Command1_Click()

i = 1

While i <= 10

Print i

i = i + 1

Wend

End Sub

It will print 1 to 10 on the form. Here Body of loop will executed repeatedly if the condition is true until it false, i.e. same as do while loop.

For…..Next

Syntax

For <Loopcontrolvariable>  = I^st to Last <Step Incrementt/Decrement>

<Body of loop>

Next <Loopcontrolvariable>

Eg:-

Private Sub Command1_Click()

For i = 1 To 10 Step 1

Print i

Next i

End Sub

It will print 1 to 10 on the form. Here Body of loop will executed repeatedly if the value of loop control variable equal to 10.

Nesting of control structures

If one control structure contains another control structure inside in its body is called nesting of control structures.

It may be

A decision within another decision

A decision within another loop

A loop within another loop

A loop within another decision

Eg:-

Private Sub Command1_Click()

For i = 1 To 10

If i <= 5 Then

Print i

End If

Next i

End Sub

          It will print 1 to 5 on the form.

Exit statement

It is used to exit from a loop conditionally.

Eg:-

Private Sub Command1_Click()

For i = 1 To 10

Print i

If i = 5 Then Exit For

Next i

End Sub

It will print 1 to 5 on the form then exit from the for loop statement.

Goto statement

It is used to jump from one line of statement to another statement unconditionally.

Eg:-

Private Sub Command1_Click()

a = Text1.Text

b = Text2.Text

If b = 0 Then

GoTo Error

Error:

MsgBox "Division is not possible"

Else

c = a / b

MsgBox c

End If

End Sub

It will produce the divided result if b not equal to zero otherwise displays a message box with message "Division is not possible".

End statement

It indicates the termination of a VB program. It closes the running windows of VB Program.

Private Sub Command1_Click()

End

End Sub