An Object-Oriented Approach to Programming Logic and Design

1. An Object-Oriented Approach to Programming Logic and Design Chapter 4 Understanding Structure

2. Objectives • Describe the role of structure in object-oriented methods • Draw flowcharts • Understand unstructured spaghetti code • Understand the three basic structures of sequence, selection, and loop • Build structured methods An Object-Oriented Approach to Programming Logic and Design

3. Objectives (continued) • Use a priming read • Understand the need for structure • Recognize structure • Describe two special structures: • case • do until An Object-Oriented Approach to Programming Logic and Design

4. The Role of Structure in Object-Oriented Methods • Recall that classes can contain non-static instance methods such as • public get: to retrieve the object’s data • public set: to set values for the object’s data • Otherpublicmethods: to accomplish tasks using the object’s data An Object-Oriented Approach to Programming Logic and Design

5. The Role of Structure in Object-Oriented Methods (continued) • An application can also contain static methods • No object exists for these methods, but they may manipulate objects instantiated from prewritten classes • All methods should be structured methods An Object-Oriented Approach to Programming Logic and Design

6. The Role of Structure in Object-Oriented Methods (continued) • A structured method: • Follows a specific set of rules for logical design • Has a single entry and exit point An Object-Oriented Approach to Programming Logic and Design

7. Drawing Flowcharts • Symbols on a flowchart: • Lozenge: racetrack-shaped; marks the beginning or end of a method • Annotation symbol: three-sided box attached to flowchart by a dashed line; provides details for a step • Processing statement: rectangle; contains an action taken • Input/output: parallelogram; denotes data coming in from or going out on a device An Object-Oriented Approach to Programming Logic and Design

8. Drawing Flowcharts (continued) An Object-Oriented Approach to Programming Logic and Design

9. Understanding Unstructured Spaghetti Code • Spaghetti code: unstructured code that is confusing and complex due to poor structure • Flowchart of spaghetti code shows crossed flow paths with no clear path from beginning to end • Unstructured code is difficult to read, understand, and modify An Object-Oriented Approach to Programming Logic and Design

10. Understanding Unstructured Spaghetti Code (continued) An Object-Oriented Approach to Programming Logic and Design

11. Three Basic Structures of Sequence, Selection, and Loop • Structure –a basic unit of programming logic • All programs are composed of 3 structures: • Sequence • Selection • Loop An Object-Oriented Approach to Programming Logic and Design

12. Three Basic Structures of Sequence, Selection, and Loop (continued) • Sequence structure: performs one or more actions in sequence, with no branching, skipping, or looping; continues step by step An Object-Oriented Approach to Programming Logic and Design

13. Three Basic Structures of Sequence, Selection, and Loop (continued) • Selection structure: allows one of two or more alternative paths to be taken • if-then-else when only 2 alternatives if hours-worked is more than 40 then calculate overtimePay else calculate regularPay An Object-Oriented Approach to Programming Logic and Design

14. Three Basic Structures of Sequence, Selection, and Loop (continued) • Loop structure: allows repetition or iteration • Asks a question and performs an action if a certain answer is given, then asks the question again. • Also called a while loop or a while-do loop while testCondition continues to be true, do someProcess An Object-Oriented Approach to Programming Logic and Design

15. Building Structured Methods • All logic problems can be solved with only the sequence, selection, and looping structures • Structures can be stacked, one after another • Structures can be nested, one within another An Object-Oriented Approach to Programming Logic and Design

16. Building Structured Methods An Object-Oriented Approach to Programming Logic and Design

17. Building Structured Methods (continued) An Object-Oriented Approach to Programming Logic and Design

18. Building Structured Methods (continued) • Block: group of statements that execute as a single unit • All pseudocode statements inside a block should be indented • Indentation in pseudocode reflects the logic shown graphically in a flowchart An Object-Oriented Approach to Programming Logic and Design

19. Building Structured Methods (continued) An Object-Oriented Approach to Programming Logic and Design

20. Building Structured Methods (continued) • endif always matches the most recent if that is not already matched • endwhile always matches with the most recent while that is not already matched An Object-Oriented Approach to Programming Logic and Design

21. Building Structured Methods (continued) An Object-Oriented Approach to Programming Logic and Design

22. Building Structured Methods (continued) • Each structure has 1 entry and 1 exit point • Other structures may attach only at an entry or exit point An Object-Oriented Approach to Programming Logic and Design

23. Using a Priming Read • Priming read (or priming input): the first read or data input statement that occurs before and outside the loop that handles the rest of the input • Priming read is required to keep a method structured An Object-Oriented Approach to Programming Logic and Design

24. Using a Priming Read (continued) An Object-Oriented Approach to Programming Logic and Design

25. Using a Priming Read (continued) • Rules for a structured loop: • You ask a question • If the answer indicates a task is to be performed, do so • After you perform the task, go back to ask the question again An Object-Oriented Approach to Programming Logic and Design

26. Using a Priming Read (continued) Example: It’s structured, but doesn’t work! An Object-Oriented Approach to Programming Logic and Design

27. Using a Priming Read (continued) Example: It works, but isn’t structured! An Object-Oriented Approach to Programming Logic and Design

28. Using a Priming Read (continued) Example: It works, and it’s structured! An Object-Oriented Approach to Programming Logic and Design

29. Using a Priming Read (continued) public void numberDoubling() numeric userNumber numeric answer while userNumber not = 0 answer = userNumber * 2 print answer input userNumber endwhile return An Object-Oriented Approach to Programming Logic and Design

30. Understanding the Reasons for Structure • Why structured methods are better: • Clarity: structured methods are less confusing • Professionalism: it is the expected standard in industry today • Efficiency: today’s programming languages are built expecting structure • Maintenance: easier to modify programs later • Modularity: facilitates reuse of modules An Object-Oriented Approach to Programming Logic and Design

31. Understanding the Reasons for Structure (continued) An Object-Oriented Approach to Programming Logic and Design

32. Understanding the Reasons for Structure (continued) An Object-Oriented Approach to Programming Logic and Design

33. Recognizing Structure • Example: Is this flowchart segment structured? • Yes, it has a loop and a selection within the loop An Object-Oriented Approach to Programming Logic and Design

34. Recognizing Structure (continued) • Example: Is this flowchart segment structured? • No, it is not constructed from the 3 basic structures An Object-Oriented Approach to Programming Logic and Design

35. Recognizing Structure (continued) • To untangle spaghetti code, pull one “strand” at a time and follow it • Let’s “untangle” this flowchart  An Object-Oriented Approach to Programming Logic and Design

36. Recognizing Structure (continued) Untangling Example: Steps 1 & 2 An Object-Oriented Approach to Programming Logic and Design

37. Recognizing Structure (continued) Untangling Example: Step 3 – the “No” side of Question B An Object-Oriented Approach to Programming Logic and Design

38. Recognizing Structure (continued) Untangling Example: Step 4 – the “Yes” side of Question B An Object-Oriented Approach to Programming Logic and Design

39. Recognizing Structure (continued) Untangling Example: Step 5 – left side of Question D: repeat step C to untangle it An Object-Oriented Approach to Programming Logic and Design

40. Recognizing Structure (continued) Untangling Example: Step 6 – right side of Question D leads to the end An Object-Oriented Approach to Programming Logic and Design

41. Recognizing Structure (continued) An Object-Oriented Approach to Programming Logic and Design

42. Describing Two Special Structures: case and do until • case structure: allows more than 2 alternative paths • dountil loop: an alternative to the while loop • case and do until are not needed, but are convenient, acceptable structures An Object-Oriented Approach to Programming Logic and Design

43. The case Structure • Use a case when there are several distinct values for a variable, each of which requires a different action • case eliminates the need for a set of nested if statements An Object-Oriented Approach to Programming Logic and Design

44. The case Structure (continued) Example: using nested if statements An Object-Oriented Approach to Programming Logic and Design

45. The case Structure (continued) Example: using a case statement instead An Object-Oriented Approach to Programming Logic and Design

46. The do until Loop • do until loop is similar to the while loop, but tests the condition at the end of the loop • while loop tests the condition at the beginning of the loop; If the answer is no, the action is not performed • dountil loop performs the action, then tests the condition; the action is always performed at least once An Object-Oriented Approach to Programming Logic and Design

47. The do until Loop (continued) An Object-Oriented Approach to Programming Logic and Design

48. The do until Loop (continued) • while loop pseudocode: pay bills while there are more bills to pay pay bills endwhile • do until loop pseudocode: do pay bills until all bills are paid An Object-Oriented Approach to Programming Logic and Design

49. The do until Loop (continued) Comparison: using a do until loop An Object-Oriented Approach to Programming Logic and Design

50. The do until Loop (continued) Comparison: using a while loop An Object-Oriented Approach to Programming Logic and Design