Overview

• Background.
• Quiz topics.
• Sample quiz questions.
• Additional student questions.

Background

• Particularly because CSC 151 is taught in a workshop-style format, we offer regular review sessions to give students other ways to explore the material.
  
  • Review sessions also give a chance for you to ask questions about upcoming or past assignments.
• Class mentors offer evening sessions on Wednesday and Thursday evenings.
• I offer one session a week, Thursdays at 10 a.m. (I teach at 3pm on Thursdays; otherwise I would be offering one then instead.)
• Traditionally, my review sessions are the least organized of the bunch. I list recent topics, students ask questions about those topics, and I do my best to help them better understand.
• Some students have asked that review sessions focus more on the kinds of questions that might appear on the quiz, so I often begin with a list of such questions.
• I post most of what I say in my review session to the Web for your reference (and for those who can't make it to the review session).
  • If no one shows up, I don't hold a review session, and so no record is likely to exist (other than preliminary notes, if I've taken any).
  • Thank you to the 3 CC and 3 SR students who attended so that this week's review session was held!

Quiz Topics

• The parts of an algorithm.
• Very basic Scheme.
• The philosophy of Linux.
• The class syllabus.

Sample Quiz Questions

The Parts of an Algorithm

List the core building blocks of algorithms.

• You have to start somewhere, so you work with some basic kinds of values and operations.
• You are doing more than one operation, so you need a way to sequence operations.
• Algorithms typically require data to work with, which we term input or parameters.
• Along the way, you may find it useful to name intermediate results, which we call variables (even though they rarely vary).
• Sometimes you have to make choices in your algorithm. We call these conditionals.
• Sometimes you want to do an action again and again and again. We call this repetition.
• It is often helpful to name a sequence of steps. We call this a subroutine.

For each building block of algorithms, identify a corresponding part of the almond butter and preserves algorithm.

• Basic values and operations: Pick up something; orient something
• Sequencing: Need to open the bag before we take out bread. The order in which we gave instructions is the order in which we did them.
• Input/parameters: The bread, the jelly, and the nut butter.
• Variables: "Dominant hand". "The bread on the plate"
• Conditionals: If it's a screw-top jar ...; if it's a pop-top jar ...; if it's neither, slam it on the desk to reach the goop inside. If there's not enough peanut butter on the bread, add more.
• Repetition: Turn the lid of the jar counter-clockwise until the lid separates from the jar; spread the goop until it evenly coats one side of the bread.
• Subroutines: We used the same set of instructions to take out the first and second slice of bread. "Spread goop" works for jelly or nut butter. "Open jar"

Basic Scheme: Evaluate

What output will you get when you type the following instructions?

> (+ 3 4)
7
> (define a 4)
; nothing shows up, but whenever we type `a` we get the value 4
> (* a 2)
8
> (square a)
You idiot.  square is not defined. (or some other error messsage)
> (sqrt a)
2
> (a + 5)
I'm sorry, 4 is not an operation
> (sqrt (a))
I'm sorry, 4 is not an operation.  Didn't you learn that yet?
> (+a 5)
I'm sorry, +a is not an operation.  (Or some less intuitive error
message)
> (+ a b)
We don't have b defined yet
> (string-append "a" "b")
"ab"
> (string-append a a)
4 is not a string

Basic Scheme: Write

Translate the following mathematical expressions (using PEMDAS) into Scheme form. (PEMDAS - parentheses, exponent, multiplication/division, addision/subtraction)

32 + 17 * 2 
> (+ 32 (* 17 2))

(32 + 17) * 2 
> (* (+ 32 17) 2)

32 + 17 * 2 / 4
> (+ 32 (* 17 (/ 2 4)))

32 + 18 / 2 / 4
> (+ 32 (/ 18 (/ 2 4))) ; NO
> (+ 32 (/ (/ 18 2) 4))
> (+ 32 (/ 18 2 4)) ; OKAY, BUT CONFUSING

11 + 12 + 13
> (+ 11 12 13)

Assorted Questions

What are the two meanings of "free" in "free software"?

• Doesn't cost anything.
• Free to look at how it is built. "Free as in freedom"

How often do we have quizzes in this class?

• Every Friday!

How is this class likely to be different from other classes at Grinnell?

• A variant of workshop style?
• More work than any other two courses put together
• Take-home exams
• Large!
• ???

Additional Questions

Note: Ordering in Scheme is different! We do steps inside-out, rather than left-to-right (or PEMDAS or whatever)

(* 3 (+ 4 5))

How do you deal with ambiguity, such as "spread the goop", which could be either repetition ("spread the goop until evenly coated") or subroutine ("spread the goop" works for any goop)?

Fairly leniently, since there is some ambiguity involved. We often give you labels, and you use each label once.

What is the relationship between subroutines and basic operations?

Subroutines are the operations you write, basic operations are the ones the computer/language already knows.

You assume I know the basic operation "twist", from that, you build the subroutine "open jar"

You assume I know the basic operation *, from that, you build the subroutine "square"