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CS3 Fall 2005

CS3 Fall 2005. Lecture week 13: Introduction to the Big Project. todo. Fix dates in calendar here, and in project description in ucwise. Fix printing and sequencing slide. Midterm #2. Any questions?. Midterm #2. Average: 30.6 Std. Dev. 11.5. Midterm #2 – question 3.

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CS3 Fall 2005

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

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

  3. Midterm #2 Any questions?

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

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

  9. 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…

  10. Lets see the projects in action

  11. 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

  12. 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)))

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

  14. 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…

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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 …)

  20. 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

  21. List selectors • car • Like first • cdr • Like butfirst

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

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