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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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Fundamental concept
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
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
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
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
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
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
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
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
    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 … Next Syntax 1(no skipping)

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

    <Statements>

    Next <counter>


    Example
    Example:

    Dim UserName as string

    Dim times as integer

    Username = “Paul”

    Lbloutput.text = “ ”

    For times = 1 to 10 step 1

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

    Next times


    Example1
    Example:

    Dim UserName as string

    Dim times as integer

    Username = “Paul”

    Lbloutput.text = “ ”

    For times = 1 to 10

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

    Next


    For next syntax 2 with skipping decrement
    For … Next Syntax 2(with skipping/decrement)

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

    <Statements>

    Next <counter>


    Example 1
    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
    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
    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
    Syntax: Do while …. Loop

    Do while <condition>

    <statement>

    <statement>

    Loop


    Example2
    Example:

    Private Sub Command1_Click( )

    Dim N As Integer

    N = 0

    Do While N < 10

    N = N + 1

    Print N

    Loop

    End Sub


    Example3
    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
    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 … Loop While Syntax

    Do

    < statement >

    < statement >

    < statement >

    Loop while < condition >


    Example4
    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
    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 … Loop Syntax

    Do until < condition >

    < statement >

    < statement >

    Loop


    Example5
    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
    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.



    Activity 1 2
    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


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