Controll Structures

7/28/2019 Controll Structures

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Control Structures

If left unchecked by control-flow statements,a program's logic will flow through statements fromleft to right, and top to bottom.

Control structures allow you to control the flow ofyour program's execution.

IT Department - National Institute of Education End Show


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Control Structures

Selection-(Branching)

Repetition-(Looping)

Sequences



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Selection (Branching)

IF

Select Case

Goto

Control Structures



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Control Structures

Repetition

For Next

Do While

Do until



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Control Structures

Branching statements are used to cause certainactions within a program if a certain condition ismet.

If Then statement

If (Balance Check) < 0 Then Print "You are overdrawn"

Syntax

-Selection

IF Statement



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Control Structures -Selection

Private Sub Command1_Click()

Dim Number As Integer

Number = InputBox("Enter value")

If Number > 50 Then MsgBox("Pass")

End Sub



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Control Structures

If Then and End If blocks allows multiplestatements:

If Then and End If blocks

IF thenstatement 1

statement 2

................

statement n

end if

Syntax



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If Then end if

Private Sub Command1_Click()number = Text1.TextIf number Mod 2 = 0 Then

MsgBox ("Even")End If

End Sub



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Dim balance As Currency

Dim check As Currency

balance = 5490.98

check = 9678.78

If balance - check < 0 Then

Print "You are overdrawn"

Print "Authorities have been notified"

End If

End Sub

If Then end if



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If Then else end if

Here, the same two lines are printed if you areoverdrawn (Balance - Check < 0), but, if you are not

overdrawn (Else), your new Balance is

computed.

If Balance - Check < 0 ThenPrint "You are overdrawn"

Print "Authorities have been notified"

ElseBalance = Balance - Check

End If



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If Then else end if

Write a program to read marks and display

Grade as Follows

Marks>=75 Grade is A

Marks=65 Grade is B

Marks =55 Grade is C

Other wise Grade is D



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Dim Marks As IntegerDim Grade As StringMarks = InputBox("Enter marks")If Marks >= 75 Then

Grade = "A"ElseIf Marks >= 65 Then

Grade = "B"ElseIf Marks >= 55 Then

Grade = "C"ElseIf Marks >= 0 Then

Grade = "D"

Else MsgBox ("Invalid marks")End IfMsgBox (Grade)

End Sub



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Select Case testexpression

[Case expressionlist1

[statementblock-1]]

[Case expressionlist2

[statementblock-2]].

.

.

[Case Else

[statementblock-n]]

End Select

Select Case



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Select Case

Visual Basic provides the Select Case structure as

an alternative to If...Then...Else for selectively

executing one block of statements from amongmultiple blocks of statements. A Select Case

statement provides capability similar to the

If...Then...Else statement, but it makes codes more

readable when there are several choices.



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Select Case

Write a program to read a number and display whether odd or

even using select case


Dim number As Integer

number = InputBox("Enter integer")

Select Case number Mod 2

Case 0

MsgBox ("Even number")

Case 1MsgBox ("Odd Number")

End Select

End Sub



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Select Case

Write a program to read marks and display

Grade as Follows

Marks>=75 Grade is A

Marks=65 Grade is B

Marks =55 Grade is C

Other wise Grade is D

IT Department - National Institute of Education

End Show


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Select Case


Dim Marks As IntegerMarks = InputBox("Enter integer")

Select Case Marks

Case 75 To 100

MsgBox ("A")

Case 65 To 74MsgBox ("B")

Case 55 To 64

MsgBox ("C")

Case 0 To 54

MsgBox ("D")Case Else

MsgBox ("Invalid Marks")

End Select

End Sub



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.

The GoTo Statement

Another branching statement.

The format is GoTo Label, whereLabel is a labeled line.

Labeled lines are formed by typing the

Label followed by a colon.



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Line10:

..Goto Line10



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disp1: number = InputBox("Enter Number between 0 to 100")

If number


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Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"

Print "Sri Lanka"

End Sub

For...Next



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When you know you must execute

statements a specific number of times,

ForNext loop is the better choice.

For...Next



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For loop uses a variable called a

counterthat increases or decreases

in value during each repetition of the

loop.

Cont



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Forcounter= startToend[Step increment]

statement

Statement

statement

.

Next [counter]

The syntax is:



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The arguments counter, start, end, and incrementare

all numeric.

The incrementargument can be either positive or

negative.

startmust be less than or

equal to endor the statements in the

loop will not execute.

Ifincrementis positive,

For i=1 to 100 step 5

Cont



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startmust be greater than or

equal to endfor the body of the loop to execute.

If Step isn't set, then incrementdefaults to 1.

In executing the For loop, Visual Basic:Sets counterequal to start.

Ifincrementis negative

For i=100 to 1 step -5

Cont



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In executing the For loop, Visual Basic:

1. Sets counterequal to start.

2. Tests to see ifcounteris greater than end.

If this is so, Visual Basic exits the loop.

5. Repeats steps 2 through 4.

3. Executes the statements.

4. Increments counterby 1 or by increment, if it's

specified.



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FORcounter

=start

TOend

[STEPincrement

]statement

Statement

statementNEXT [counter]

1 2

3

4

Set counterequal to startTest to see ifcounteris greater than end.

Executes the statements.

Increments counterby 1 or by increment, if it's specified.

Cont



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FORcounter

=start

TOend

[STEPincrement

]statement

Statement


1 2

3

4

Cont



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FOR counter= startTO end[STEP increment]

statement

Statement


1 2

3

4

Cont



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statement

Statement


1 2

3

4

Cont



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statement

Statement


1 2

3

4

Cont



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statement

Statement


1 2

3

4

Cont



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FOR counter= 1 TO 5

PRINT COUNTER

NEXTcounter

1 2

3

4

Sets counterequal to 1

Tests to see ifcounteris greater than 5

1

Increments counterby 1 or by increment, if it's specified.

Cont


C t


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Write a program to Sri Lanka Five times


Dim i As Integer

For i = 1 To 10

Print "Sri Lanka"

Next

End Sub

Cont



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2. Write a program to read 15 numbers and display

the average.

1. Write a program to read ten numbers and display the total;



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Write a program to Display the Following numbers



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Dim i,j as Integer

For i = 1 To 3

For j = 1 To 4Print i,j

Next j

Next i

End Sub



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

0 0



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 0



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 0i


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 0i


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 1



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 1



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 1

j


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 1

j


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Dim i,j as Integer

For i = 1 To 3

For j = 1 To 4Print i ,j

Next j

Next i

End Sub

i j

1 1

1 1



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 1

1 1



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 2

1 1



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 2

1 1

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 2

1 1

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 2

1 11 2



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 2

1 11 2



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 3

1 11 2



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 3

1 11 2

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 3

1 11 2

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 3

1 11 21 3



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 3

1 11 21 3



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 4

1 11 21 3



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 4

1 11 21 3

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 4

1 11 21 3

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 4

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4

IT Department - National Institute of EducationIT Department - National Institute of Education End Show


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

1 5

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 5

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 5

1 11 21 31 4

i


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 5

1 11 21 31 4

i


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 1

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 1

1 11 21 31 4



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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 1

1 11 21 31 4

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 1

1 11 21 31 4

J


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Dim i,j as Integer

For i = 1 To 3


Next j

Next i

End Sub

i j

2 1

1 11 21 31 4

J


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Write a program to read 6 number and

Display totalPrivate Sub Command1_Click()

Dim i As Integer


Dim tot As Integer

For i = 1 To 6

number = InputBox("Enter number")

tot = tot + number

Next

MsgBox (tot)

End Sub



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2. Write a program to read 15 numbers and

display the average.

1. Write a program to read ten numbers and

display the total.


Do while


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Do while

Do...Loop, the statements execute as long as

the condition is True:

Do...Loop

Use a Do loop to execute a block of statementsan indefinite number of times.

There are several variations of the

Do...Loop statement,

but each evaluates a numeric condition

to determine whether to continue execution.


Do while


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Do While conditionstatements

Loop

When Visual Basic executes this Do loop,it first tests condition.

If it's True (nonzero),

Visual Basic executes the statements and then goes

back to the Do While statement and

tests the condition again.

Do while


Write a program to Display Sri lanka 10 times


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Dim i As Integer

Do While i < 10

Print "Sri Lanka"

i = i + 1

Loop

End Sub


Do while


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Ifcondition is False (zero),

it skips past all the statements.

Do while


Dim counter As Integer

counter = 1

Do While counter


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executes the statements first

and then tests condition after each execution.This variation guarantees

at least one execution ofstatements:

Do

statementsLoop While condition

Another variation of the

Do...Loop statement

Do while




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Dim i As Integer

Do

Print "Sri Lanka"

i = i + 1

Loop While i < 10

End Sub



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Dim Sum As Integer

Sum = 0

Do

Sum = Sum + 5

Print Sum

Loop While Sum


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Do Until conditionstatements

Loop

Do Until Loop

Do Until/Loop structure will

execute until condition isfalse


Do Until Loop Cont


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Do Until Loop Cont

Private Sub Command1_Click()Dim Sum As Integer

Sum = 0

Do Until Sum >= 50

Sum = Sum + 5

Print Sum

Loop

End Sub


Do Until Loop Cont


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Do Until Loop Cont

Private Sub Command1_Click()Dim Sum As Integer

Sum = 0

Do

Sum = Sum + 5

Print Sum

Loop Until Sum >= 50

End Sub


Control structures


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Two other variations are analogous to theprevious two,

except that they loop as long

as conditionis False rather than True.

Loop zero or more times Loop at least once

Do Until condition

statementsLoop

Do

statementsLoop Until condition

Documents

Controll Structures