Iteration Control Structure

1. Iteration Control Structure Fourth Quarter

2. 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.

3. Parts of the Loop • Body of the Loop : Set of statements which is repeated. • Loop Exit Condition: condition to be tested before each repetition.

4. 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.

5. Step : the manner on how the records are to be processed in the given file. Proper sequencing is needed (ascending or descending).

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

7. 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

8. 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?

9. 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?

10. 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

11. 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

12. 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

13. 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.

14. For … Next Syntax 1(no skipping) For <counter > = <Start> to <Stop> Step <Step> <Statements> Next <counter>

15. 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

16. 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

17. For … Next Syntax 2(with skipping/decrement) For <counter > = <Start> to <Stop> Step <Step> <Statements> Next <counter>

18. Example 1 Dim counter as integer Lbloutput.text = “” For counter = 10 to 1 step -1 lbloutput.text = lbloutput.text & chr(13) & counter Next

19. Example 2 Dim counter as integer Lbloutput.text = “” For counter = 9to 1 step -2 lbloutput.text = lbloutput.text & chr(13) & counter Next

20. 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

21. Syntax: Do while …. Loop Do while <condition> <statement> <statement> Loop

22. Example: Private Sub Command1_Click( ) Dim N As Integer N = 0 Do While N < 10 N = N + 1 Print N Loop End Sub

23. 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

24. 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

25. Do … Loop While Syntax Do < statement > < statement > < statement > Loop while < condition >

26. Example: Private Sub Command1_Click( ) Dim N As Integer N = 0 Do N = N + 1 Print N Loop While N < 10 End Sub

27. 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

28. Do Until … Loop Syntax Do until < condition > < statement > < statement > Loop

29. Example: Private Sub Command1_Click( ) Dim N As Integer N = 0 Do Until N >= 10 N = N + 1 Print N Loop End Sub

30. 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.

31. Hands – On Session

32. 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:

33. Filenames: • Activity No.1 • 4Act12CN • Activity No.2 • 4Act22CN