1. Jaeki Song ISQS6337 JAVA Lecture 04 Control Structure - Selection, and Repetition -

2. Jaeki Song ISQS6337 JAVA Outline Selection –if statement –switch statement Repetition –while statement –for statement

3. Jaeki Song ISQS6337 JAVA Control Structure A standard progression of logical steps to control the sequence of statement execution Basic control structures –Sequence –Selection –Repetition

4. Jaeki Song ISQS6337 JAVA Flowcharts Often use either flowcharts or pseudocode to plan a program’s logic –Pseudocode Write down the steps required to accomplish a given task using English –Flowcharts Write the steps you need in diagram form, as a series of shapes connected by arrows

5. Jaeki Song ISQS6337 JAVA Sequence Logical Control Structure This is the overriding control structure. Instructions are carried out in order or sequence. Action can be inputs, processes, or outputs Action 1 Action 2 Action 3

6. Jaeki Song ISQS6337 JAVA Selection Logical Control Structure I Instructions are executed depending on the outcome of a test; also called branching –If….then….else Condition Action 1Action 2 Condition is FALSE Condition is TRUE

7. Jaeki Song ISQS6337 JAVA Decision Making Looks Like rain Wash car Test cancelled Study for test NO YES

8. Jaeki Song ISQS6337 JAVA if Structure Making a decision involves choosing between two alternative courses of action based on some value –The value upon which a decision is made is a boolean value boolean expression Resulting action Comparison operators (relational operator) are results in boolean values

9. Jaeki Song ISQS6337 JAVA Comparison Operators < <= > >= = == = != less than less than or equal to greater than greater than or equal to equal to not equal to The boolean expression, e.g. (userResponse = = ‘Y’), must appear within parentheses

10. Jaeki Song ISQS6337 JAVA The if Statement Branch only if the condition is True Format if (relational expression) { block of statements to be executed if relational expression is true }

11. Jaeki Song ISQS6337 JAVA The if Statement The else Clause Branch in one direction if test is True, another if False. Format: if (relational expression) { block of statements executed when True } else { block of statements executed when False }

12. Jaeki Song ISQS6337 JAVA Example if (studentGrade >= 60) System.out.println (“ Passed”); else System.out.println (“Failed”) Grade >= 60 Print “passed” true false

13. Jaeki Song ISQS6337 JAVA The if Statement Nesting if Statements if and if-else statements can contain any valid JAVA statements, including other if or if-else statements. Placing an if or if-else within an if or if-else is called nesting. When nesting if-else statements within on another, care must be taken. The pairing of if’s and else’s can be tricky!

14. Jaeki Song ISQS6337 JAVA If..else and if…else if Statement if (StudentGrade >= 90) System.out.println (“A”); else if (StudentGrade >= 80) System.out.println (“B”); else if (StudentGrade >= 70) System.out.println (“C”); else if (StudentGrade >= 60) System.out.println (“D”); else System.out.println(“F”); if (StudentGrade >= 90) System.out.println (“A”); else if (StudentGrade >= 80) System.out.println (“B”); else if (StudentGrade >= 70) System.out.println (“C”); else if (StudentGrade >= 60) System.out.println (“D”); else System.out.println(“F”);

15. Jaeki Song ISQS6337 JAVA Example: Grade

16. Jaeki Song ISQS6337 JAVA AND and OR Operators Use AND operator (&&) within a boolean expression to determine whether two expression are both true. –Both boolean expression must be true before the action in the statement can occur if (itemSold > 3 && totalValue > 1000) bonus = 50;

17. Jaeki Song ISQS6337 JAVA AND and OR Operators Use OR operator (||) when you want some action ot occur even if only one of two conditions are true // using two ifs if (itemSold > 100) bonus = 50; else if (totalValue > 1000) bonus = 50; // Using OR operator If (itemSold > 100 | | totalValue > 3000) bonus 50;

18. Jaeki Song ISQS6337 JAVA Selection Logical Control Structure II Case control structure –Allow more than two choices when the condition evaluated Condition Action 1 Condition4 is TRUEConditio3 is TRUEConditio2 is TRUEConditio1 is TRUE

19. Jaeki Song ISQS6337 JAVA The switch Statement An alternative to the series of nested if statements Uses four keywords –switch: starts the structure and is followed immediately by a test expression enclosed in parentheses. –case: is followed by one of the possible values for the test expression and a colon –break: optionally terminates a switch structure at the end of case –default: optionally is used prior to any action that should occur if the test variable does not match any case

20. Jaeki Song ISQS6337 JAVA The switch Statement if (year == 1) System.out.println (“Freshman”); else if (year = =2) System.out.println (“Sophomore”); else if (year = =3) System.out.println (“Junior”); else if (year = =4) System.out.println (“Senior”); else System.out.println(“ Invalid year”); Switch (year) { case 1: System.out.prinln (“Freshman”); break; case 2: System.out.prinln (“Sophomore”); break; case 3: System.out.prinln (“Junior”); break; case 4: System.out.prinln (“Senior”); break; default: System.out.println (“Invalid year”); }

21. Jaeki Song ISQS6337 JAVA The switch Statement break statement –You can leave out the break statement in a switch structure When you omit the break, if the program find a match for the test variable, the all statements within the switch statement form that point forward will execute

22. Jaeki Song ISQS6337 JAVA Example: Shipping Option

23. Jaeki Song ISQS6337 JAVA The Repetition Structure Repetition Pre-Test Repetition –Sentinel Value Loop Post-Test Repetition –Fixed-Count Loop Nested Loops

24. Jaeki Song ISQS6337 JAVA Repetition Logical Control Structure Allows for repeated execution of a set of statements based upon the outcome of a condition or test. –Also known as looping or iteration. Two components of a repetition structure: –Relational Expression or Test –Loop Body

25. Jaeki Song ISQS6337 JAVA Relational Expressions Relational expression –Set up as for Selection. –Always evaluates to either True (any non-zero value) or False (a zero value). Body is executed as long as the test is True. Exit the loop when test is False.

26. Jaeki Song ISQS6337 JAVA Loop Body Is usually a block of code Contains instructions that reflect the task to be repeatedly performed; Can contain any valid Java statements Usually includes code so that the test will eventually prove False (or an infinite loop condition will result).

27. Jaeki Song ISQS6337 JAVA Pretest Repetition: while Statement Condition is tested before the body is ever executed. –Use a while loop to execute a body of statements continuously while some condition continues to be true. Boolean expression false Loop body true

28. Jaeki Song ISQS6337 JAVA The while Statement while loop can be used to implement pretest repetition Format: while (relational expression) { statements executed while test is True } Example While (4 >2) System.out.println(“hello”) Infinite loop

29. Jaeki Song ISQS6337 JAVA The while Statement To prevent an infinite while loop –The loop control variable is initialized –The loop control variable is tested in the while statement –The body of the while statement must take some action that alter the value of the loop control variable Example loopCount = 1; while (loopCount < 3) { System.out.println (“Hello”); loopCount = loopCount + 1; }

30. Jaeki Song ISQS6337 JAVA Increment and Decrement Operators Increment Operators (all add 1 to the variable) int icount = 0; icount = icount + 1 icount += 1 icount++ ++icount Decrement Operators (all subtract 1 from the variable) int dcounter = 0; dcounter = dcounter - 1 dcounter -= 1 dcounter-- --dcounter

31. Jaeki Song ISQS6337 JAVA Example Class Average Program

32. Jaeki Song ISQS6337 JAVA Pretest Repetition; the for Statement for loop is counted loop and can also be used to implement pretest repetition –Use a while loop when you need to perform a task some predetermined number of times –A loop that executes a specific number of time is a counted loop Format: for(initialization; expression; altering) { statements executed while condition is True } Example for (int counter = 1; counter <=10 ; counter++) Control variable name and initial value Increment of control variables Loop condition and final value

33. Jaeki Song ISQS6337 JAVA Output Format Pakage from java.text: import java.text.DecimalFormat; DecimalFormat precisionTwo = new Decimal Format (“0.00”) Pakage from javax.swing import javax.swing.JTextArea; JTextArea outputTextArea = new JTextArea (11,20) Number of rows Number of columns

34. Jaeki Song ISQS6337 JAVA Example: The for Repetition

35. Jaeki Song ISQS6337 JAVA Posttest Repetition: The do-while Statement Condition is tested after the body is executed; Body is always executed at least once; Often used for data validation, where data is validated as it is interactively entered.

36. Jaeki Song ISQS6337 JAVA The do-while Statement do-while loop is used to implement posttest repetition Format: do { statements executed while condition is True } while (relational expression);