--- title: Eboard 04 Introducing lists number: 04 section: eboards held: 2018-01-29 link: true --- CSC 151.01, Class 04: Introducing lists ======================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Lab * Debrief Preliminaries ------------- ### News / Etc. * Welcome back to our permanent version of Shelby. * Thanks for keeping the room neat. * When you speak in class, please say your name first. * I'm already behind on grading. I apologize. * I talk fast. I try to slow myself down by writing a lot. But it could can be difficult. Question for you (I'll close my eyes for the answer): How is my speed? * Please try to slow down a bit. * It's fine, or at least acceptable. * Please try to speed up. ### Upcoming work * [Assignment 2](../assignments/assignment02) due TOMORROW night. * Readings (online), due before class Wednesday. * [Defining your own procedures](../readings/procedures) * [How Scheme evaluates expressions, take 2](../readings/scheme-eval-2) * [Lab writeup for class 4](../writeups/writeup04), due before class Wednesday * Exercise 6. * "CSC 151.01 Writeup for Class 4 (Your Name)" * Mail to * [Flash cards](../flashcards/flashcards02) due at 5pm Wednesday. * See below for additional details. * Submit ten flash card Q&As via email with a subject of "CSC 151.01 Flashcards (Week 2)" ### About flash cards * A chance to summarize some key points or confusing points. * A potential study mechanism. * Both aspects have documented effect on learning basic concepts. * And you can't do the complex stuff in CSC 151 unless you know the "language": vocabulary, syntax, etc. * Examples: * What is `(round 3.4)`? * How does `1/2` differ from `0.5`? * How does `1/2` differ from `(/ 1 2)`? * What are the parameters to `substring`? * What is `(substring "Hello" 1 3)`? * Answers: * `3.0` * `1/2` is exact; `0.5` is inexact. * `1/2` represents a number. `(/ 1 2)` represents a computation. * `(substring string start-pos after-end-pos)` * `"el"` * I will provide you with a summary of the questions and answers. * You may use them in whatever way you consider best. * Usually about a week's worth of work (WFMW) ### Extra credit (Academic/Artistic) ### Extra credit (Peer) * Posse Plus Retreat Recap, February 6 at 11am, JRC 101. ### Extra credit (Misc) ### Other good things ### Questions Why do you write some strange symbols, such as backticks, when you write the eboards? : I use a "language" called Markdown to format my text; it allows me to make the "pretty" Web pages without too much effort. Why am I getting stupid errors from `map1`, like "that's not an integer", when it is? : Sam needs examples. I want to do the self-checks on my own computer. What do I do? : Download DrRacket. (Free.) : Add the CSC151 package. (See day 1 lab.) : Email me an example of it not working. Can I do without the `(require csc151)`. : Probably, but I don't know what it is. How should we separate the different examples in HW 1? : In a way you think it will be easy for the grader to understand. Is there a citation format you prefer? : I like APA. : I care more about the act of citing than the precise format. A URL suffices. Lab --- Note: You can comment stuff out by surrounding it with pound-bar and bar-pound. ``` #| Look, DrRacket will ignore this. So I can type incorrect stuff (3 + 4), examples, and more. |# ``` Keyboard shortcuts * Ctrl-up - Previous command * Esc-p - Previous command * Ctrl-down - Next command Debrief ------- * Which of the following is easier for you to do: count the number of elements of a list by hand or write `(length lst)`? *Take advantage of what the computer can do!* * Using `length` can also lead to more general solutions. * I'm happy to see that some of you are checking the answers (e.g., on the calculator you carry with you). * I wrote `reduce`. You've already seen that I sometimes lack competenence (e.g., in building Web sites). I could have written an incorrect definition of `reduce`. * There are at least three ways to add 2 to each element of a list. * `(map increment (map increment lst))` * `(map (o increment increment) lst)` * `(map + lst (make-list (length lst) 2))` * Some of you are already encountering the issue of "I should be able to write *this*, but I can't." Welcome to working within limits. * You will learn better ways to write things like "add 1.5" in the next lab. A solution to problem 5 ``` (map min (make-list (length ratings) 6) (map max (make-list (length ratings) 0) ratings)) ``` Theme of next few weeks: What we can do with individual values, we can do with lists of values.