Iteration Control Structure Fourth Quarter
Feb 24, 2016
Iteration Control Structure
Fourth Quarter
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.
Fundamental Concept
Body of the Loop : Set of statements which is repeated.
Loop Exit Condition: condition to be tested before each repetition.
Parts of the Loop
Start : the starting or the beginning point of the loop.
One may start with first or the last record in the file.
Parts of the Loop: 3 S
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
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
Control Variable
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. 1
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?
Problem No. 2
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
Counters
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 ValueNew Value
Accumulators
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
Looping Statements
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 Statement
For <counter > = <Start> to <Stop> Step <Step>
<Statements>
Next <counter>
For … Next Syntax 1(no skipping)
Dim UserName as stringDim times as integerUsername = “Paul”Lbloutput.text = “ ”For times = 1 to 10 step 1Lbloutput.text = lbloutput.text & chr(13) & Username
Next times
Example:
Dim UserName as stringDim times as integerUsername = “Paul”Lbloutput.text = “ ”For times = 1 to 10 Lbloutput.text = lbloutput.text & chr(13) & Username
Next
Example:
For <counter > = <Start> to <Stop> Step <Step>
<Statements>
Next <counter>
For … Next Syntax 2(with skipping/decrement)
Dim counter as integerLbloutput.text = “”For counter = 10 to 1 step -1 lbloutput.text = lbloutput.text & chr(13) & counterNext
Example 1
Dim counter as integerLbloutput.text = “”For counter = 9 to 1 step -2 lbloutput.text = lbloutput.text & chr(13) & counterNext
Example 2
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
Do while ….. Loop
Do while <condition><statement><statement>
Loop
Syntax: Do while …. Loop
Private Sub Command1_Click( )Dim N As Integer
N = 0Do While N < 10
N = N + 1Print N
LoopEnd Sub
Example:
Example:Private Sub Command1_Click( )Dim N As Integer
N = 0Do While N < 10
N = N + 1Print N
LoopEnd Sub
Loop Statement
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
Do< statement >< statement >< statement >
Loop while < condition >
Do … Loop While Syntax
Private Sub Command1_Click( )Dim N As Integer
N = 0Do
N = N + 1Print N
Loop While N < 10End Sub
Example:
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
Do until < condition >< statement >< statement >
Loop
Do Until … Loop Syntax
Private Sub Command1_Click( )Dim N As Integer
N = 0Do Until N >= 10
N = N + 1Print N
LoopEnd Sub
Example:
DO WHILE / DO UNTIL
Display numbers from
1 to 10
Do While N < 10N = N + 1Print N
Body of Loop will be executed as long as the condition is TRUE.
Display numbers from 1 to 10
Do Until N >= 10N = N + 1Print N
Body of Loop will be executed as long as the condition is FALSE.
Hands – On Session
a. Make a program that will display this output on the form:
b. Make a program that will display “Patience is a Virtue” 5 times.
Activity 1 & 2
Filenames:◦Activity No.1
4Act12CN◦Activity No.2
4Act22CN