1. CS 180 Problem Solving and Object Oriented Programming Fall 2010 Notes for Week 7: Oct 4-8, 2010 Aditya Mathur Department of Computer Science Purdue University West Lafayette, IN, USA http://www.cs.purdue.edu/homes/apm/courses/CS180Fall2010/ 1.Exam 1: Performance 2.Project 1: Performance 3.Feedback for Week 6 4.Arrays 5.Demo 6.Incremental program development 7.Multi-dimensional arrays 8.Visual depiction of arrays 10/4 This Week: 10/6

2. Readings and Exercises for Week 7 Readings: Chapter 6: 6.1, 6.2, 6.3, 6.4 Exercises: 6.3, 6.4, 6.5, 6.7 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 72

3. Special help session Thursday Oct 7, 5-7pm: Special help session in the B158 Sunday October 10: No help session. Enjoy your break! 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 73

4. Special class Sunday October 17: 4-5:30pm For those who have not been able to perform well on Exam 1 and/or Project 1. Send me email if you wish to attend. Bring your laptops. 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 74

5. Lunch meeting When: Thursday October 7, 2010. Noon-1:30pm Where: Ford Dining Hall Meet: Upstairs in the Ford dining hall Attendees: All who signed up for September 30 and October 7 Look forward to seeing you! 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 75

6. Performance: Exam 1 Part B: Count: 231 Average: 59.7 Max Score: 70/70 scored by 40 students Median: 63.0 Standard deviation: 11.95 10/6/2010 Overall: Count: 231 Average: 393.3/480 Max Score: 480 obtained by 11 students Median: 417.6 Standard deviation: 78.2 ©Aditya Mathur. CS 180. Fall 2010. Week 76

7. Performance: Exam 1: Histogram 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 77

8. Exam 1: Common mistakes: Q1 10/6/2010 Incorrect types for coordinates (int instead of float or double) 3 to -5 points Incorrect or forgotten formatting -3 points Code in main() method instead of in constructor -2 points Incorrect coding of the distance formula -10 to –20 points ©Aditya Mathur. CS 180. Fall 2010. Week 78

9. Exam 1: Common mistakes: Q2 10/6/2010 Incorrect random number generation (-2 to -15 points) Minor syntax errors (-1 to -2 points). Code in main() instead of constructor (-3 points). Incorrect datatype for min, max (-2 points) Incorrect class structure, like constructor inside main() (-2 to -5 points) Not *reading* min and max from user (-5 points) Incorrect if conditions (-2 to -5 points) ©Aditya Mathur. CS 180. Fall 2010. Week 79

10. Performance: Project 1 Total graded: 222 Average: 60.7 Max score: 64 by 81 students 59—63: 105 students Median: 62 Standard deviation: 7.23 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 710

11. Robots in labs Please take a survey in this week’s lab Please do not toast us! The robots were intended to give you some “thrill” and help in understanding the challenges of programming embedded systems. Unfortunately, the Ridge Soft robots turned out to be unreliable devices! 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 711

12. Feedback for Week 6 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 712

13. Q1. The lab exercises were useful (Use scale of 1-10: 10 most useful, 1 not useful at all) (a)8-10 (b)4-7 (c)1-3 (d)Missed Week 6 lab 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 713

14. Q2. The recitation exercises were useful (Use scale of 1-10: 10 most useful, 1 not useful at all) (a)8-10 (b)4-7 (c)1-3 (d)Missed 6 recitation 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 714

15. Q3. The recitation instructor was helpful. (Use scale of 1-10: 10 most helpful, 1 not helpful at all) (a)8-10 (b)4-7 (c)1-3 (d)Missed week 6 recitation 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 715

16. Q4 Exam 1 was (a)Very easy (b)Somewhat easy (c)Somewhat tough (d)Tough (e)Very tough 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 716

17. Q5. I have completed Project 2 (a)Yes (b)Nearly complete (c)Not started 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 717

18. Q6. So far I am liking the course (a)A lot (b)Somewhat (c)Not sure 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 718

19. Arrays 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 719

20. Arrays: What are these? 10/6/2010 A homogeneous collection of variables or objects. All elements of an array are of the same type. Examples: Array of integers where each integer represents the age of a patient. Array of cars where each element of the array denotes a specific car. Array of flowers where each element of the array denotes a flower. ©Aditya Mathur. CS 180. Fall 2010. Week 720

21. Arrays: When to use? 10/6/2010 When there is a need to retain data in memory for efficient processing. Data is created once and used many times. Examples: Array of flights: Search for a specific flight Array of cars: Search for a specific car, or find the average price. Array of laptops: find the cheapest laptop ©Aditya Mathur. CS 180. Fall 2010. Week 721

22. Declaring an Array 10/6/2010 int [] age; /* age refers to an array of integers; e.g. age of people in a database*/ double [] weight; /* weight refers to an array of doubles; e.g. weights of items shipped*/ String [] name; /* name refers to an array of elements each of type String; e.g., names of people in a database*/ Indicates age is an array variable ©Aditya Mathur. CS 180. Fall 2010. Week 722

23. Declaring an Array: of objects 10/6/2010 Bird [] bird; /* Bird refers to a class; bird is an array where each element is an object of type Bird. */ Aircraft [] fleet; /* Aircraft refers to a class; fleet is an array where each element is an object of type Aircraft. */ ©Aditya Mathur. CS 180. Fall 2010. Week 723

24. Creating an Array 10/6/2010 int [] age=new int[10]; /* age is an array of 10 elements each of type int*/ double [] weight=new double[100]; /* weight is an array of 100 elements each of type double*/ String [] name=new String[15]; /* name is an array of 15 elements each of type String*/ Aircraft [] fleet=new Aircraft[150]; /* fleet is an array of 150 elements each of type Aircraft*/ ©Aditya Mathur. CS 180. Fall 2010. Week 724

25. Accessing an array element: general syntax 10/6/2010 name [expression] Index, starts from 0, must be an intName of the array Examples: age[i]; // 0<=i<10 fleet[k]; // 0<=k<150 weight[i+j]; // 0<=(i+j)<100 Note: First element of an array is located at index 0. ©Aditya Mathur. CS 180. Fall 2010. Week 725

26. Accessing an array element 10/6/2010 int [] age=new int[10]; int p= age[5]; /* p gets element at index 5 of array age*/ double [] weight=new double[100]; double hisWeight=weight[i]; /* hisWeight gets the element of weight at index i*/ Aircraft [] fleet=new Aircraft[150]; Aircraft rental=fleet[k]/* rental gets the element of fleet located at index k */ ©Aditya Mathur. CS 180. Fall 2010. Week 726

27. Assigning a value to an array element 10/6/2010 int [] age=new int[10]; age[i]=15; /* (i+1) th element of age becomes 15. */ double [] weight=new double[100]; weight[k]=weight[k]-10; /* (k+1) th element of the weight is decremented by 10.*/ Aircraft [] fleet=new Aircraft[150]; fleet[i]=new Aircraft(); /* (i+1) th element of fleet gets a new Aircraft */ int [] age={-15, 20, 30} // All elements initialized ©Aditya Mathur. CS 180. Fall 2010. Week 727

28. Iterating through elements of an array 10/6/2010 In many problems we need to iterate through all or a few of the elements of an array. Such an iteration is accomplished by using a for or a while loop. ©Aditya Mathur. CS 180. Fall 2010. Week 728

29. Problem: Find average 10/6/2010 int ageSum=0; // Initialize sum of all ages int [] age=new int[10]; // Create array of int to hold ages for( int i=0; i<age.length; i++){ ageSum=ageSum+age[i]; // Accumulate ages } double average=ageSum/(double)age.length; ©Aditya Mathur. CS 180. Fall 2010. Week 729

30. Problem: Search in an array 10/6/2010 String [] wList={"Emilio", "Semion", "Osama"}; Scanner s=new Scanner (System.in); String wanted=s.next(); // Get name to be searched boolean found=false; // Not yet found int next=0; // Points to the first element in wanted list while(next<wList.length && !found) { if(wanted.equals(wList[nextItem])) // Compare found=true; // If equal then we have found the wanted! else next++; // else point to the next item on the list }//End of loop ©Aditya Mathur. CS 180. Fall 2010. Week 730

31. Problem: Search in an array 10/6/2010 if(found) System.out.println(wanted+ " exists in database"); else System.out.println(wanted+ " not in database") } // End of program ©Aditya Mathur. CS 180. Fall 2010. Week 731

32. Problem: Statement 10/6/2010 A plant biology lab maintains a collection of leaves. The lab director wishes to create a simple database that contains several entries. Each entry is a plant name, type of its leaf, and a brief description of the leaf in the collection. Example: WhitePine Needle NA Heather Compound NA Write a program that reads data from a file as mentioned above and allows a user to search for a tree in the database. ©Aditya Mathur. CS 180. Fall 2010. Week 732

33. Problem: Understanding 10/6/2010 A plant biology lab maintains a collection of leaves. From where can my program read the leaf data? If it is in a file, then what is the name of that file? The lab director wishes to create a simple database that contains several entries. How much data is available? Write a program that reads data from a file as mentioned above and allows a user to search for a tree in the database. In what form will the user input a request? ©Aditya Mathur. CS 180. Fall 2010. Week 733

34. 10/6/2010 Java program for plant biology lab. Incremental stepwise development! ©Aditya Mathur. CS 180. Fall 2010. Week 734

35. Tasks 10/6/2010 1.Read plant collection data from a file 2.Provide search service to the user 3.Exit with a bye bye message when done. ©Aditya Mathur. CS 180. Fall 2010. Week 735

36. Let us assume…. 10/6/2010 1.LeafCollection class is available 2.It provides the following methods: createCollection() searchService() 3.Leaf class is available. It provides the following methods: public void getTree(); public void getLeafType(); public void getDescriptionType(); ©Aditya Mathur. CS 180. Fall 2010. Week 736 Why did we make the above assumptions?

37. Overall design: Classes 10/6/2010 LeafCollectionServer Main server Initiates actions ©Aditya Mathur. CS 180. Fall 2010. Week 737 Uses Leaf private String parentPlant; private String leafType; private String leafDescription; public String getTree(); public String getLeafType(); public String getDescriptionType(); Uses

38. LeafCollectionServer 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 738 Back to the Java program. Version 1.0.

39. LeafCollection: Design 10/6/2010 Question: How should we store leaf collection data? Recall: For each leaf, we have its parent tree, its type, and its description. ©Aditya Mathur. CS 180. Fall 2010. Week 739 This is a class. Provides two methods: createCollection() searchService() But before we can write these methods we must have a way to read from a file and save in memory all the data about the collection!

40. LeafCollection: Design Question 10/6/2010 Question: How should we store leaf collection data? Recall: For each leaf, we have its parent tree, its type, and its description. ©Aditya Mathur. CS 180. Fall 2010. Week 740 Answer: ??

41. LeafCollection 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 741 Back to the Java program. Version 2.0.

42. Leaf: Design: Attributes 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 742 Recall, for each leaf, we have the following available data: Name of parent tree Name of the leaf Description

43. Leaf: Design: Methods 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 743 Recall, for each leaf, we have the following available data: public String getLeafName(); public String getTreeName(); public String getDsecription();

44. Leaf class 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 744 Back to the Java program. Version 3.0.

45. 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 745 Arrays: Visual representation

46. Single dimensional array: Example 1 10/6/2010 int [] cloudyDays=new int [12] // average cloudy days/month ©Aditya Mathur. CS 180. Fall 2010. Week 746 Anchorage, Alaska 0 1 2 3 4 5 6 7 8 9 10 11 [19 18 18 18 20 20 22 21 21 21 20 21 ] cloudyDays[0]cloudyDays[5]cloudyDays[11] Index Data

47. Single dimensional array: Example 2: Declaration 10/6/2010 Car [] carStock=new Car [5] // Cars at a dealership ©Aditya Mathur. CS 180. Fall 2010. Week 747 public class Car{ String make; // e.g. Ford String model; // e.g. Fusion int year; // e.g. 2011 long msrp; // e.g. US$23145 Picture carPic; }

48. Single dimensional array: Example 2: Visual 10/6/2010 Car [] carStock=new Car[5] // Cars at a dealership ©Aditya Mathur. CS 180. Fall 2010. Week 748 CS180 Dealership in West Lafayette 0 1 2 3 4 [ ] carStock[0] carStock[4] Index Object Reference {Porsche, Boxster Spyder, 2011, 72000, } } {Ford, fusion, 2011, 23150 } ….

49. 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 749 Arrays: Multidimensional

50. Example 1 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 750 FLAGSTAFF 12 11 12 9 7 4 9 8 5 7 8 11 PHOENIX 10 9 8 6 3 2 4 4 3 4 6 9 TUCSON 10 9 9 6 4 3 9 7 4 5 6 10 WINSLOW 12 10 9 7 5 4 8 6 4 6 8 10 YUMA 9 6 6 4 2 1 3 3 2 3 5 8 MEAN MONTHLY CLOUDY DAYS IN ARIZONA J F M A M J J A S O N D int [][] cloudyDays=new int [5][12 ] rowscolumns 0 1 2 3 4 016897245 31110 What is the value of cloudyDays[1,8]?

51. Declaration 10/6/2010 Cars [] inventory=new Car [3][]; 3 rows and undefined number of columns Each row represents make of a car and column represents models ©Aditya Mathur. CS 180. Fall 2010. Week 751 Chevy0 Honda1 Toyota2 AvalancheTraverse AccordFitCivic CamryCorollaRav4 021

52. Arrays: Typical errors 10/6/2010 Index out of bounds [Run time error] int [] a=new int [10]; a[i]=x; // i is greater than 9 or less than 0 Element not initialized [Compile time error] String [] name; name[i]=“Bob”; // element not initialized ©Aditya Mathur. CS 180. Fall 2010. Week 752

53. Week 7: October 4-8, 2010 Hope you enjoyed this week! Questions? Contact your recitation instructor. Make full use of our office hours. 10/6/2010©Aditya Mathur. CS 180. Fall 2010. Week 753