Held: Friday, 29 August 2003
Today we begin to consider the structure and content of
- Lessons from PB and J.
- Common parts of an algorithm.
- Some administrative details.
- Lab: Getting Started in the MathLAN.
Left for you to fill in the details.
- As you may have noted, there are some common aspects to algorithms.
That is, there are techniques that we use in many of the algorithms
- It is worthwhile to think about these algorithm parts
because we can rely on them when we write new algorithms.
- As we write algorithms, we like to name things.
- Sometimes we use long names, such as
the piece of bread in
your dominant hand.
- Sometimes, we use shorter names, such as
- As we start to write more formal algorithms, we will need
techniques for noting which names we are using and indicating
what they name (and, sometimes, what kind of thing they name).
- We call these named values variables, even though they
don't always vary.
- Many algorithms take data as input (and generate other data
- Our PBJ algorithm takes bread, jelly, and such as input.
find square root algorithm would take a number as input.
look up a telephone number algorithm might take a phone
book and a name to lok for as inputs.
- In each case, the algorithm should works on many different inputs.
- The algorithm works as long as the input is
reasonable (we can't find the square root of a piece of
bread and we can't make a PBJ sandwich with tunafish).
- We call these inputs parameters.
- At times, our algorithms have to account for different conditions, doing
different things depending on those conditions.
- In our PBJ algorithm, we might check whether the jar of peanut butter
is open or what kind of lid is on the jelly jar. We call such
- Conditionals typically take either the form
if some condition holds then do something
- Here's a slightly more complex form
if some condition holds then do something otherwise
do something else
- At times, we need to decide between more than two possibilities.
Typically, we organize those as a sequence of tests (called guards)
and corresponding things to do.
- At times, our algorithms require us to do something again and again.
- In our PBJ algorithm, we may have had to turn the twisty-tie again
and again until it was untwisted.
- We call this technique
- Again, repetition takes many forms.
- We might do work until we've reached a desired state.
- We might continue work as long as we're in some state.
- We might repeat an action a fixed number of times.
- You can probably think of many other forms of repetition.
- Many algorithms require common actions for their operation.
- For example, to make N sandwiches, you benefit from knowing how to make
- To make a peanut butter and jelly sandwich, it helps to know
how to spread something on bread.
- We can write additional algorithms for these common actions and
use them as part of our broader algorithm.
- We can also use them in other algorithms.
- We call these helper algorithms
- Computer Science 151 has a number of goals
- To introduce you to fundamental ideas of computer science: abstraction,
algorithms, and data
- To enhance your problem-solving skills and give you experience
in formal representation of problems and solutions.
- To introduce you to two primary paradigms of problem solving:
functional and imperative.
- To give you some programming skills that you can apply to problems
in other disciplines.
- I expect and hope that you will find CSC151 different from any class
you've taken in the past.
- We use a different format than many classes: a collaborative,
workshop-style format. (You may have seen this format in other
introductory science courses; we do it somewhat differently.)
- Computers and computer science also require you to think differently.
I expect that you'll exercise some brain cells you may have forgotten
you have. (And after all, isn't liberal arts education an exercise
in thinking in as many ways as you can?)
- Like most computer science courses, CSC151 will have both theoretical
and practical components. I hope you will enjoy relating the two.
- This semester's section of 151 will be somewhat different from the ones I've taught in the past.
- I've dropped a section on graphics that no one seemed to like all that much.
- I've added a section having to deal with the cool exhibit at the gallery.
- You may have noted that I said that we'll study two paradigms
of problem solving.
- Over the years, computer scientists have designed (discovered?)
a number of techniques for looking at how to write solutions
to problems. There are four basic ones.
- We'll visit each in terms of making cookies (or at least we'll
- Imperative: Solutions are a collection of basic
instructions with some additional sequencing.
- Sift dry ingredients.
- Stir 50 times.
- Object-Oriented: Solutions are a collection of
- Head chef: Hand bowl of ingredients to mixing sous-chef.
- Sous-chef: Upon receiving bowl of ingredients, mix.
- Functional: Solutions consist of function definitions
and function applications. It's often useful to think of
a function as a form of filter: it converts its input to
- The mixer converts separate ingredients into a consistent mush.
- The oven converts raw dough to cooked dough.
- Declarative: Solutions consists of collections of
- To bake cookies, you cook at 375 degrees F for 8 to 10 minutes.
- Chocolate chip cookies contain ...
- Some people wonder why we need computer languages like Scheme, Pascal,
C, Java, and the ilk.
- In part, it's probably because the computer elite want to maintain
their sense of superiority over the masses.
- In greater part, it's because English and other
can be ambiguous. At the very least, they have many similar structures
that are interpreted very differently. Consider the classic pair of
- Time flies like an arrow.
- Fruit flies like a banana.
- Remember: Computers are sentient and malicious.
It often seems that they'll do their best to misinterpret whatever it
is you write.
- Please refer to the course web site
for more details. (They won't be available until Monday, though.)
- Teaching philosophy: I support your learning.
- Attendance: I expect you to attend every class. Let me know
when you'll miss class and why.
- Grading: I'm a hard grader. I don't grade everything.
- Course web.
- Daily work
- Attend class, work on lab and participate in discussion.
- Finish the lab in the evening.
- Do the reading for the next class in the evening.
- The exams
- Three take-home exams during the semester. Plan to spend
six to eight hours on each one.
- An optional final to make up for a bad exam grade.
- Take all three exams anyway.
- The labs
- Available online.
- Being re-written as the semester progresses.
- I'll require more formal writeups of a few labs a semester.
- The homework
- About five.
- One makeup at the end of the semester.
- Academic honesty
- Core to the academic process.
- My basic policy: Don't cheat.
- The college's basic policy: Cite carefully.
- Significant breakdowns in CSC151 last semester.
- Read my handout on
academic honesty carefully.
Thursday, 28 August 2003 [Samuel A. Rebelsky]