# Iteration Control Structure - PowerPoint PPT Presentation

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Iteration Control Structure. Fourth Quarter. Fundamental Concept. Involves loops or cycles Loops : means that a process may be repeated as long as certain condition remains true or remains false. Means “ multiple processing ”

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Iteration Control Structure

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## Iteration Control Structure

Fourth Quarter

### Fundamental Concept

• Involves loops or cycles

• Loops: means that a process may be repeated as long as certain condition remains true or remains false.

• Means “multiple processing”

• Provides means of repeating a part of instruction without rewriting the part again and again.

### Parts of the Loop

• Body of the Loop : Set of statements which is repeated.

• Loop Exit Condition: condition to be tested before each repetition.

### Parts of the Loop: 3 S

• Start : the starting or the beginning point of the loop.

• One may start with first or the last record in the file.

Step : the manner on how the records are to be processed in the given file.

Proper sequencing is needed (ascending or descending).

Stop : the ending point . It is normally represented in a form of a conditional expression, thus, a decision symbol is used in the flowchart

### Control Variable

• Is a variable that defines the starting, ending point and step of a looping statement.

• It should be a variable that will uniquely identify all the records in the file.

• It is a representation of a field in the record. The shorter the value, the better is the field

### Problem No. 1

• Draw a flowchart that will read the grades in PT, CS and QS of student. Compute the average of the student. Print the name and the computed average.

• Input :

• Process:

• Output:

• Will there be multiple processing? How many times the inputting, processing and outputting will be performed? WHY?

Problem No. 2

• Draw a flowchart that will read the grades in PT, CS and QS of all the students in the class of II - ____. Compute the average of all the students. Print the names and the computed averages.

• Input :

• Process:

• Output:

• Will there be multiple processing? How many times the inputting, processing and outputting will be performed? WHY?

### Counters

• Are used to literally count the number of times a portion of the flowchart is traced.

• Need to be initialized / prepared prior to its use or application.

• The operation involved is “addition”

• The increment value is a constant

• Example: C = C + 1

Increment Value

Current Value

New Value

### Accumulators

• A numerical value that collects the result of a repeated mathematical operation.

• Used to keep a running total of an item / the operation involved is “addition”.

• Need to be initialized / prepared prior to its use or application.

• The incremental value is a “variable” (subjected to change)

• Example: S = S + N

Increment Value

• Current Value

New Value

### Looping Statements

• Executes a group of instructions repeatedly

• Has 3 Structures:

• For ……. Next

• Do …….. Loop : has three types:

• Do While …. Loop

• Do Until …. Loop

• Do …… Loop while

• While ….. Wend

• ### For …. Next Statement

• Executes a section of the code a specified number of times.

• Begins with the “for” statement and ends with the “next” statement.

• Can only be used if the programmer knows the number of times the loop must be performed prior to its execution.

### For … Next Syntax 1(no skipping)

For <counter > = <Start> to <Stop> Step <Step>

<Statements>

Next <counter>

### Example:

Dim times as integer

Lbloutput.text = “ ”

For times = 1 to 10 step 1

Lbloutput.text = lbloutput.text & chr(13) & Username

Next times

### Example:

Dim times as integer

Lbloutput.text = “ ”

For times = 1 to 10

Lbloutput.text = lbloutput.text & chr(13) & Username

Next

### For … Next Syntax 2(with skipping/decrement)

For <counter > = <Start> to <Stop> Step <Step>

<Statements>

Next <counter>

### Example 1

Dim counter as integer

Lbloutput.text = “”

For counter = 10 to 1 step -1

lbloutput.text = lbloutput.text & chr(13) & counter

Next

### Example 2

Dim counter as integer

Lbloutput.text = “”

For counter = 9to 1 step -2

lbloutput.text = lbloutput.text & chr(13) & counter

Next

### Do while ….. Loop

• Most common statement among the do ..loop statements

• Test condition appears at the TOP of the loop

• As long as the test condition is TRUE, the block of code in the body of the loop will be continuously executed

• When the test condition becomes FALSE, the loop terminates.

• Condition before iteration

### Syntax: Do while …. Loop

Do while <condition>

<statement>

<statement>

Loop

### Example:

Private Sub Command1_Click( )

Dim N As Integer

N = 0

Do While N < 10

N = N + 1

Print N

Loop

End Sub

### Example:

Private Sub Command1_Click( )

Dim N As Integer

N = 0

Do While N < 10

N = N + 1

Print N

Loop

End Sub

Loop Statement

### Do ….. Loop While

• The test condition appears at the bottom of the loop.

• When the test condition stays TRUE, the loop still executes until it becomes false

• Condition after iteration

### Do … Loop While Syntax

Do

< statement >

< statement >

< statement >

Loop while < condition >

### Example:

Private Sub Command1_Click( )

Dim N As Integer

N = 0

Do

N = N + 1

Print N

Loop While N < 10

End Sub

### Do Until …. Loop

• Test condition also appears at the TOP of the LOOP.

• Executes the block of statements as long as the test condition is FALSE

### Do Until … Loop Syntax

Do until < condition >

< statement >

< statement >

Loop

### Example:

Private Sub Command1_Click( )

Dim N As Integer

N = 0

Do Until N >= 10

N = N + 1

Print N

Loop

End Sub

### DO WHILE / DO UNTIL

Display numbers from

1 to 10

Do While N < 10

N = N + 1

Print N

Body of Loop will be executed as long as the condition is TRUE.

Display numbers from

1 to 10

Do Until N >= 10

N = N + 1

Print N

Body of Loop will be executed as long as the condition is FALSE.

Hands – On Session

### Activity 1 & 2

• Make a program that will display “Patience is a Virtue” 5 times.

• Make a program that will display this output on the form:

• Filenames:

• Activity No.1

• 4Act12CN

• Activity No.2

• 4Act22CN