--- title: Eboard 14 Discussion of exam 1 number: 14 section: eboards held: 2017-09-25 --- CSC 151.03, Class 14: Discussion of exam 1 =========================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Common issues * Exercise 2 * Exercise 6 * Exercise 5 * Exercise 4 * Remaining issues ### News / Etc. * New partners. * Please make sure to return your computer cards to the jar. * I'm glad to be back; I'm sorry that I missed classes. * 70 exams x 6 problems + admin x 5 min = approx 2400 minutes or 40 hours. I'll get exams back to you *next* Monday. ### Upcoming Work * [Writeup for class 13](../writeups/writeup13) due TONIGHT at 10:30 p.m. * Exercise 6 * To: * Subject: CSC 151.03 Writeup 13 (YOUR NAMES) * There is no writeup for today's class. * [Assignment 4](../assignments/assignment04) due Tuesday at 10:30 p.m. * Reading for Wednesday's class: [Displaying data](../readings/displaying-data) (Not yet available) ### Extra credit (Academic/Artistic) * CS Table, Tuesday: Casual chat * Google technical résumé talk, Tuesday at 4pm, Science 3821 * Scholars Convocation, Thursday at 11am: Wilson Okello on "Living in the Wake of Crisis" ### Extra credit (Peer) * Upcoming Women's soccer matches ### Extra Credit (Misc) _None at the moment._ ### Other Good Things * Volleyball Wednesday * GHS Homecoming - North of GHS on Thursday at 4pmish. ### Questions There's something weird on the lab writeup. Can we look at it? : Check your guard for the unknown case. It should probably be something like `(not (real? (cadr entry)))` rather than `(equal? (cadr entry) "")`. Problem 4 of the assignment suggests that we should test it on other schedules. Does that mean we should write our own? : Yes. Common issues ------------- * When to ask for help. Early and often. * Work on the six-P style documentation. The form *is* important. Postconditions tell you not just type, but value. * Postconditions are what the procedure is guaranteed to do * What got extra credit? * Really nice tests. * The occasional good joke. * Some implementations that made me say "cool" * "There's more to life" belongs only on your cover sheet. * I really do care that you use the template file. * Formatting. Please hit ctrl-i before submitting. Problem 2 --------- We'll look at documentation and code. ``` ;;; (length newlst) < (length lst) ; BAD POSTCONDITION ``` * We can't guarantee that. start could be 0 and finish could be (length lst) * It's insufficient. We could, for example, just filter out some elements and achieve the goal. We could just drop a few elements. We could make a list of zeros. We could return null. `(define sublist (lambda (lst start finish) null))` Thinking about edge cases is important for preconditions. Can the original list be empty? What is the smallest/largest value for start? What is the smallest/largest value for finish? Problem 6 --------- We'll walk through one approach to solve it. There were others. Problem 5 --------- We'll walk through one approach to solve it. There were others. Problem 4 --------- What should you test? What are your answers? (I'll then add my own.) * [An alternate to Is this the list I get? is to ask whether the sum is correct.] * If you remove all the odd numbers from a list of odds numbers, you should get the empty list. * All even numbers. * Alternating odd and even numbers. * Only 0's. Lots of numbers, including 0. * Big numbers (highly positive, highly negative) * Evens at the front * Odds at the front * Evens in the middle * Odds at the middle * Evens at the end * Odds at the end * Inexact numbers; NO! The preconditions forbid this. Tests on things that don't meet the preconditions are dangerous. * Positive and negative (mixed) * Really big lists * `(check-equal? (sort (remove-odds (iota 10000))) (map (section * <> 2) (iota 5000)))` * `(check-equal? (remove-odds (append (make-list 10000 5) (list 2) (make-list 20000 -3))) (list 2))` * Duplicate values We'll continue with the documentation. Why is this not a sufficient postcondition? ``` ;;; Postconditions: ;;; (length no-odds-lst) <= (length lst) ```