--- title: Eboard 01 An introduction to algorithms number: 01 section: eboards held: 2018-01-22 link: true --- CSC 151.01, Class 01: An introduction to algorithms ==================================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Introduction - What is CS? * Exercise - An everyday algorithm * Debriefing on exercise * Common parts of an algorithm Preliminaries ------------- ### News / Etc. * Welcome to CSC 151! * I'm Sam (or SamR) * Your class mentors are Sally and Shelby * You should have received four handouts at the start of class. * A playing card * The [CS Department Academic Honesty Policy](http://www.cs.grinnell.edu/academic-honesty-policy) * [Assignment 1](../assignments/assignment01) * A packet of readings * Reading: [Algorithms](../readings/algorithms) * Reading: [Linux](../readings/linux) * Reading: [The DrRacket Programming Environment](../readings/drracket) * Reading: [Beginning Scheme](../readings/beginning-scheme) * Since it's the first day of class, I'll be taking attendance. (It will take a few weeks for me to learn all of your names. * "Hi, my name is FORENAME SURNAME." * "You can call me PRIMARY NAME." * "If you must address me by surname, you can call me Mr./Ms./Mx./[nothing] SURNAME." * I'm from ... * Optional: "My pronouns are ...." * Disclaimers * Sam is slightly hard of hearing. * Sam is incredibly snarky. (Sam = *S*narky *a*nd *m*ean) * Contact Sam if you would like to be on the department mailing list. ### Upcoming work * [Assignment 1](../assignments/assignment01) due Tuesday night. * Readings (handed out today), due before class Wednesday. * Signed academic honesty policy due in class on Friday. * If you are uncomfortable signing it, make an appointment to chat with me. ### Extra credit (Academic/Artistic) * MLK day (+ 1 week + 1 day) event, Tuesday, 7:00 pm, JRC 101 ### Extra credit (Peer) _None yet._ ### Extra credit (Misc) * Fill out the Data Buddies survey that you received over break. ### Other good things ### Questions Introduction - What is CS? -------------------------- Write down a definition (your definition). You may be called upon to share it with the class. * The study and practice of computers. * Horrible and vague. * What does it mean to study? * Disect * Look at the individual components * Get a deeper understanding * What's a computer? * A machine, of sorts * Things that you can program * What is to program? * Write a language (that computers understand) * A program is a set of instructions that tell a computer what to do. * Do computers have to be machines? * Computer used to be a job title * Computer scientistists, when thinking about our discipline, prefer to focus more on the instructions and less on the computers. * Computer science is the study of instructions and data (representation) * How you write them to solve problems * Computer science is the study of algorithms and data structures. * "Algorithm" = "instructions for accomplishing a solution to a problem." * The class will be about writing algorithms, verifying algorithms, analyzing algorithms, and other related. * We will generally write our algorithms in an artificial language, Scheme. * Artificial languages are generally less ambiguous than English. Exercise - An everyday algorithm -------------------------------- The problem: *Write an **unambiguous** set of instructions for making a nut-butter and preserve sandwich.* * Note: Your instructions should be moderately general, in that they should work with other loaves of bread, jars of butter, and jars of preserves. * As a team based on your card number. * Your "computer" deals poorly with ambiguous instructions. * "Open" can mean many things. I have been known to open a jar by hitting it against the side of a table. Basic instructions 1. Get with your matching number group. 2. Introduce yourselves to each other. 3. Write unambiguous instructions that teach me how to make a nut butter and jam sandwich. Debriefing on exercise ----------------------- _Come up with at least four things you might have learned from doing this exercise._ * *Important*: Things will go wrong when you try to write algorithms. When they do, look back on today and laugh. * *Most common*: Be unambiguous in writing instructions. Ambiguity can often lead to errors, sometimes dangerous ones. What you think is "obvious" may not be obvious to the "computer". * Assume nothing (or at least very little) * Be specific. * Watch what your algorithm does and go back and correct mistakes before moving on. * Writing general algorithms can be much harder than writing very specific algorithms. * Good general algorithms ask about their inputs and make decisions based on those inputs. "If the bread loaf has a twisty tie, ... Otherwise, if the bread loaf has a plastic clip, ..... Otherwise, grab the ends of the bag and pull apart." * So think carefully about what the different cases may be. * There might be multiple solutions to the same problem. * Groups tend to predict problems better than individuals; group algorithm writing tends to be more successful. * Because of this, we will make you work in groups (more or less every day of class) * Don't try to write a large algorithm all at once. Write a part, try it, write the next part, try it. Etc. (Develop interactively.) Common parts of an algorithm ----------------------------