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
  • Assignment 1
  • A packet of readings
    • Reading: Algorithms
    • Reading: Linux
    • Reading: The DrRacket Programming Environment
    • Reading: 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 = Snarky and mean)
• Contact Sam if you would like to be on the department mailing list.

Upcoming work

• Assignment 1 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. https://cerp.co1.qualtrics.com/jfe/form/SV_3UH7q6TmdZ8YRPD

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 —————————-