CSC151.02 2016S, Class 55: Recap ================================ _Overview_ * Preliminaries. * Admin. * Upcoming Work. * Extra Credit. * Questions. * A few project coding notes. * The subject matter(s) of the course. * More about the subject matter(s). * Looking beyond the course. Preliminaries ------------- ### Admin * Sit where you'd like (within this room) * I will continue to bring you food (or food-like substances) until the end of the semester. * Today: Cookies. * Don't forget to show up on Friday and fill out EOCEs! * I expect to have tentative grades to you by some time Monday so that you can decide whether or not to take the final. (Folks who got extensions on exam 4 may not get grades until Tuesday night.) ### Reminders * Office hours next week * Ask me about times. * Review Sessions (go over sample exam) * Wednesday at 8pm in CS commons with Evan * Thursday at 10 am with SamR * Thursday at 8pm in CS commons with Kumar ### Upcoming Work: * I have posted a [sample final examination](../assignments/sample-final.html) to the assignments page. ### Extra Credit * Send your reports to with subject "CSC 151 Extra Credit". (Do not include the quotation marks.) * Send opportunities to me before class with subject "CSC 151 EXTRA CREDIT OPPORTUNITY!" #### Academic / Artistic * Finals week's *Inside Grinnell*. Tuesday, May 17 at noon in JRC 101. Food served. #### Peer * Humans of Grinnell College on Facebook. * May 12, 8pm, Wall Theatre, THD-117 Presents The American Family, Scenes from 20th Century American Stage Realism. * May 13, NC and company at Prairie Canary. * May 14 improv workshops 1-3pm (short form), 4-6pm (long form), Show 7:15-10:15 in Gardner lounge. * Improv study break Monday at 9pm in Burling. * Art Show Sunday, 12-1 pm, somewhere in Bucksbaum. More info coming Friday. #### Regular Peer * Social Dance Workshop Tuesdays 7:00-8:00 in Bucksbaum Dance Studio * Pun club Saturdays at 4pm in Younker * Electronic Potpourri on KDIC Fridays at Five * Space Odyssey KDIC Fridays at Six * Effective Altruism club, 2:30-3:30 Sundays in JRC 226. #### Misc ### Questions _What's up with the final?_ > It replaces your lowest exam grade, provided it is higher than your lowest exam grade. _When is the final?_ > Thursday morning. You can take the other section's on Wednesday afternoon. Here. _Is there a review session for the final exam?_ > See above. A few notes on project code --------------------------- ### Example 1 Original code (let ([petal-color (cond [(= (modulo n 10) 0) (color-name->irgb "blue")] [(= (modulo n 10) 1) (color-name->irgb "fuchsia")] [(= (modulo n 10) 2) (color-name->irgb "navy")] [(= (modulo n 10) 3) (color-name->irgb "red")] [(= (modulo n 10) 4) (color-name->irgb "indianred")] [(= (modulo n 10) 5) (color-name->irgb "lime")] [(= (modulo n 10) 6) (color-name->irgb "violet")] [(= (modulo n 10) 7) (color-name->irgb "orange")] [(= (modulo n 10) 8) (color-name->irgb "orchid")] [(= (modulo n 10) 9) (color-name->irgb "steelblue")])]) ...) Problems * Very repetitious. Seems like it has the same pattern and we should be able to do a better. * Solution: put everything in a vector and then get the appropriate element of the list. * Don't recompute the same value over and over again. (Fix with `let`) Revised code (let ([petal-color (color-name->irgb (vector-ref (vector "blue" "fuchsia" "navy" "red" "indianred" "lime" "violet" "orange" "orchid" "steelblue") (modulo n 10)))]) ...) More revised code (let* ([petal-colors (vector "blue" "fuchsia" "navy" "red" "indianred" "lime" "violet" "orange" "orchid" "steelblue")] [num-colors (vector-length petal-colors)] [petal-color (color-name->irgb (vector-ref petal-colors (modulo n num-colors)))]) ...) ### Example 2 Original code (define choose-image (lambda (num) (cond [(= 0 (mod num 53)) (image-load "/home/student/Desktop/CSC151/1charlie.jpeg")] [(= 1 (mod num 53)) (image-load "/home/student/Desktop/CSC151/2sam.jpeg")] [(= 2 (mod num 53)) (image-load "/home/student/Desktop/CSC151/3ritika.jpeg")] [(= 3 (mod num 53)) (image-load "/home/student/Desktop/CSC151/4jessica.jpeg")] ...))) Problems * Repetitious * Similar cases * Lots of image-load * ... Fixing * Probably only compute the `mod` once, either by using a `let` or by using it in another expression. * Maybe use a vector again. * Pull out the prefix from the file name. * `(define directory "/home/student/Desktop/CSC151/") * `(image-load (string-append directory "2sam.jpg")) * Naming the directory makes it easier to add images. * Naming the directory makes it a little easier to read. * Naming the directory makes it easier to change the directory. * Rename the images so that they are just a number. Improved code (define choose-image (lambda (num) (image-load (string-append "/home/student/Desktop/CSC151/" (number->string (+ 1 (mod num 53))) ".jpg")))) ### Example 3 Original code (pred (irgb (- 31 (* 31 (/ col left))) (- 95 (* 95 (/ col left))) (- 167 (* 167 (/ col left)))) (irgb (* 31 (/ (- col left) right)) (* 95 (/ (- col left) right)) (* 167 (/ (- col left) right))) (irgb (* 31 (/ (abs (- row top)) top)) (* 95 (/ (abs (- row top)) top)) (* 167 (/ (abs (- row top)) top))) (irgb (* 31 (/ (abs (- row top)) top)) (* 95 (/ (abs (- row top)) top)) (* 167 (/ (abs (- row top)) top)))) Revised code (let* ([rval 31] [gval 95] [bval 95] [mult1 (/ col left)] [mult2 (/ (- col left) right)] [mult3 (/ (abs (- row top)) top)] [color1 (irgb (- rval (* rval mult1)) (- gval (* gval mult1)) (- bval (* bval mult1)))] [color2 (irgb (* 31 mult2) (* 95 mult2) (* 167 mult2))] [color3 (irgb (* 31 mult3) (* 95 mult3) (* 167 mult3))]) (pred color1 color2 color3 color3)) The subject matter(s) of the course ----------------------------------- _I consider it important to end the semester with an overview of the primary learning goals and outcomes of the course, which we often call "the subject matter of the course." I think of CSC 151 as having a broad range of subject matters. Here's the high-level overview._ * Problem Solving. CSC 151 is about techniques for thinking about how to take a problem and develop a solution. * Computer Science: Algorithms and Data Structures. We use the approach of computer scientists, developing algorithms that solve generalized problems and arranging the data in certain ways. * Scheme. We make these issues concrete using the Scheme programming language. * Program and Software Design. And think more broadly about how to represent algorithms as programs. * General Thinking Skills. Every Grinnell class should develop skills beyond disciplinary skills. We work on a wide variety. * And Beyond. I try to provide some moral perspective on the world, too. Additional details ------------------ _With your partner, come up with three or so issues for each category. I've started with an example or two of each._ ### Problem Solving * Break a big problem up into smaller components. * Strive for comprehensive solutions. * Try different perspectives as you work on something. * Sometimes it's good to look at the big picture and get away from the details of the parentheses. * Yes! * It doesn't hurt to try ... it might just work. * Once it works, it can be useful to refine your solution. * Think about potential errors/difficult cases, and make sure that your solution works for those cases. * When you are stuck, talk to other people * Be clear when explaining! * Think about different cases ### Computer Science: Algorithms and Data Structures * Parts of an algorithm * Variables/parameters * Repetition * Subroutines * Conditionals * Pay attention to the order in which operations are done. * Basic values and operations * Recursion. * Over lists * Over files * ... * Break things up and use helper procedures. * Pairs and pair structures (lists); a way to represent info. * A lot of it is just logic that comes from normal problem solving. * The simplest answer is often the best one. * Sorting and searching ### Scheme * `define` * Numeric values and arithmetic operators * `lambda` * Order of evaluation in Scheme * Inside out * First to last * higher-order procedures: section, map, compose, * Strings and string operations ### Program and Software Design * Document * Write general procedures; take parameters! * Understand what the program should do before you write it. * Choose clear names; other people will have to read your code. * Consider efficiency! * DRY! (Don't Repeat Yourself) * Write out problems before solving them * There's more than one way to solve the same problem; you should look at multiple solutions and think which is best * Even if your first approach doesn't work, that doesn't mean that a variant won't work. ### General Thinking Skills * Working with others * Thinking on your feet * You can sometimes achieve a goal by looking at prior solutions to related goals. ### And Beyond * Grinnellians are awesome and do awesome things, you should support them. * How to handle enormous amounts of frustration. * When you are stuck, talk to other people Ask questions! * Save early and often. * Bring food! * Be compasionate, understanding, and snarky * Care! * Be moderate in what you do. Consent is necessary. * Community is important. * Real people do CS. * There is more to life than CS. * Be the driver sometimes! But switch drivers! * Laugh! * Be accommodating/accessible. ### Other issues * If you get stuck, take a break. * "The ultimate outcome of any good liberal arts education is the ability to bullshit compelling and coherently on any topic." * Get sleep, or you won't be able to phrase things coherently. * Think about the implications of asking people things in a public forum. Looking Beyond the Course ------------------------- Where do you go from here?