1. Slide 1 CS3 Fall 2005 Lecture week 13: Introduction to the Big Project

2. Slide 2 todo Fix dates in calendar here, and in project description in ucwise. Fix printing and sequencing slide

3. Slide 3 Midterm #2 Any questions?

4. Slide 4 Midterm #2 Average: 30.6 Std. Dev. 11.5

5. Slide 5 Midterm #2 – question 3 (random) isn't something you have ever seen before, because: –This procedure creates a "side-effect" –It does more than just calculate a return- value, it changes the state of Scheme so that the next call is different.

6. Slide 6 ;; check random runs (random val) n times, and returns the ;; minimum and maximum values (define (check-random val n) (check-random-helper val n 0 0)) ;; this version doesn't work! (define (check-random-helper val n cur-min cur-max) (if (<= n 0) (se cur-min cur-max) (check-random-helper val (- n 1) (if (< (random val) cur-min) (random val) cur-min) (if (> (random val) cur-max) (random val) cur-max) )))

7. Slide 7 The Big Project Three possible projects: –Database –Blocks World –Yukon You can work in partnerships You will have three weeks to work on this (it is due on the last lab) Worth 15% of you final grade

8. Slide 8 Project Check-offs There are 3 checkoffs You need to do them on time in order to get credit for the project 1.Tell your TA which project you will do and who you will do it with. 2.Show your TA that you have accomplished something. S/he will comment. 3.Show that you have most of the work done: your TA will run your code.

9. Slide 9 Nov 14Extending sentences, words to lists Nov 21Lab: Finish lists Start on the big project Thanksgiving Break – Thur/Fri Nov 28Lecture: What is CS at Berkeley? (guests) Lab: Big Project CHECKOFF #1 – Tue/Wed (beginning of lab) CHECKOFF #2 – Thur/Fri Dec 5Lecture: Summary, other languages Lab: Finish up the Project CHECKOFF #3 – Tue/Wed Project Due on Thur/Fri

10. Slide 10 Only two more lectures (after this one)… What would you like to do? –Hear about the CS major, and other courses… –Do exam-type problems… –Review…

11. Slide 11 Lets see the projects in action

12. Slide 12 Programming Style Why does it matter –Bad style gets worse in large programs –Program maintenance: 6 months later, will you know what your code does? –Code “literacy”: sharing code Remember, programming style will be considered in your project grade

13. Slide 13 What issues of style matter? Keep procedures small ! Good names for procedures and parameters Adequate comments –Above and within procedures Avoid nesting conditional statements Put tests cases in a comment block Indent to aid program comprehension Data abstraction –E.g. Don't do (bf (car '((a b) (c d)))

14. Slide 14 Of course, other issues matter Reading specifications carefully Error checking inputs, where required Adequate testing Code reuse (most useful with the database project)

15. Slide 15 Working in partnerships Highly recommended! –For those of you continuing with CS, you'll be doing this for many future projects Won't be faster, necessarily –While you are less likely to get stuck, there will be a lot of communication necessary A big benefit will be with testing Remember, only one grade is given…

16. Slide 16 Functional Programming In CS3, we have focused on programming without side-effects. –All that can matter with a procedure is what it returns –In other languages, you typically: Perform several actions in a sequence Set the value of a variable – and it stays that way –All of this is possible in Scheme.

17. Slide 17 Printing, and sequencing With Blocks World and Yukon you will need to display information. –Simply Scheme chapter 20 is nice summary. –And, all the projects have file input /output routines that you don't need to "understand", as well as user input routines.

18. Slide 18 Data structures The format of data used in these projects in a central feature –A "data structure" (abstract data type) is a specification of that format. Here, generally, lists of lists (of lists). –Accessors and constructor allow for modularity: letting parts of a program work independently from other parts.

19. Slide 19 Strings versus words One useful data structure is a string –Strings are surrounded by double quotes when printed. –Strings are a native type in Scheme. In CS3, you used words (sometimes sentences) to present names and other output to the user. –In the real world, strings are used.

20. Slide 20 Lists Lists are containers, like sentences where each element can be anything –Including, another list ((beatles 4) (beck 1) ((everly brothers) 2) … ) ((california 55) (florida 23) ((new york) 45) ) (#f #t #t #f #f …)

21. Slide 21 List constructors cons –Takes an element and a list –Returns a list with the element at the front, and the list contents trailing append –Takes two lists –Returns a list with the element of each list put together list –Takes any number of elements –Returns the list with those elements

22. Slide 22 List selectors car –Like first cdr –Like butfirst

23. Slide 23 Common list procedures Map = every Filter = keep Reduce = accumulate Null? = empty? Recursion is just the same!