Principles of Computer Science
Problem solving with the STAIR technique
- Students will learn a general problem solving
strategy that can be applied to many contexts
- Students will learn basic keyboard and mouse usage
- Students will learn to identify key problem solving
tools such as menus, on-line help, keyboard shortcuts, that are frequently present in modern software applications
- Students will apply problem solving strategies by
learning how to play unfamiliar computer games
Computers and related technology have become an undeniable
part of our daily existence. It is barely possible to live
without interacting in some way with computing technology.
The purpose of this course is to give you some tools you can
use to begin mastering technology. We will not be able to
make the impact of technology go away, but if we approach it
carefully, we can decide whether our lives are controlled
or enhanced by the computers that surround us. As the
influx of technology grows at unprecedented rates, we
quickly find that our accustomed ways of thinking may need
refinement. The universal nature of computers makes them
much more flexible than the kinds of machines we may be used
to learning. Because of this flexibility, we cannot train
ourselves to use a computer in the same way we teach
ourselves to use a more mechanical machine, such as a car or
a sewing machine. We have a well defined pattern for
learning to use these typical machines.
You figure what the machine is supposed to do,
how to make it do that job, and what to do if it isn't
working. This process works because it is possible to generalize
skills you have learned on previous machines to new machines
that do the same job. Once you learn one car or sewing machine, the
skill of driving or sewing is relatively easy to transfer to
new cars or sewing machines. You can expect any car to do
the same basic task, although the cockpit layout may be
different, the transmission may require more skill, and so
on. The same can be said of the sewing machine. You might
need to learn a new way to install thread into the machine,
but the process of sewing does not substantially change from
machine to machine. In these largely mechanical single-
purpose machines, you only have to learn one skill, although
that skill may be very complex in nature. You don't expect
cars to start flying, and you don't expect a sewing machine
to suddenly start acting like a microwave. As we will
see, computers are very different from these machines in at
least one critical way. While a car or a sewing machine is
designed primarily to do a single type of job, the computer
is capable of doing many very different kinds of jobs. The
same computer could be used as a writing tool, to simulate
the visual effects of riding a roller coaster, to play parlor games, to do
complex mathematical calculations, and to retrieve stock
market quotes from Tokyo. These things could conceivably
happen at the same time in the same computer. The skills
you would need to control a computer when it is helping you
edit documents might be very different than the skills you
use to run the roller coaster simulator. (Although the actual tasks
deep inside the computer are very similar.) It seems if we approach
learning a computer using the same learning model that we use to
understand cars and sewing machines, the learning process for
using a computer would be a very daunting task. It seems impossible
to learn how to use a computer, because each time we have it
do some new kind of job, we have to learn how to control it in
that particular context. Essentially, a computer becomes a new
kind of machine every time a new application is used with it.
Some of the applications you will
want to use a computer for in the next few years have not
yet been invented!
How then, can we hope to teach a class in how to use a
computer? Many educators have stuck with the car/sewing
machine model, treating each software application package as
a new and distinct machine. Using this model, you might
learn how to use a specific word processing package, say
WordPerfect 6.0 for Windows. You can learn how to use this
system essentially the same way you learned how to drive or
use a sewing machine. We can feed you a list of commands,
take you step by step through a number of typical processes,
and guide you carefully through your first few projects.
This is a comfortable model of learning, and it works very
well for teaching specific programs. If you need to learn
exactly how to use WordPerfect 6.0 for Windows, and that's
all you'll ever use your computer for, such an approach
would be ideal.
Unfortunately, the learning model outlined above has some
serious weaknesses when applied to learning computers and
technology. The first problem is the universality of
computers. If we teach you word processing, you have
learned something useful, but you really haven't learned
much about computers. They can do so much more than process
words. As an educated person, you will be expected to know
many other ways to use computers. We would not be doing our
job if we taught only one type of application.
Another problem is the pace with which technology changes.
It is no exaggeration to say that any software we install in
the lab today will probably be out of date by the end of the
semester. New releases of major programs come so frequently
that memorizing commands and the layout of the program is a
futile process. Things will change. You can't count on the
menu structure of a program, the control key combinations,
or anything else to stay the same.
Anther weakness in the above model is the variety of
programs that are available in any one category. If we
decide to teach you WordPerfect in our classes, and you end
up in an office which uses only Word for Windows, you could
be lost. The commands you have dutifully memorized when the
computer is running one application could do nothing at all
in a different application. It is conceivable that a
command you use to save documents in one program could be
used to delete documents in another. The potential for
confusion is obvious.
The prospects for ever learning how to use and control a
computer sound quite gloomy, but it is not nearly as bad as
it sounds. If you reflect on your classmates, family, and
friends, you can undoubtedly think of a person who can sit
down at any computer, run a program she has never seen
before, and produce amazing results. How do these people
do it? Why is it that some people can run a never - before
- seen program and make it do things for them? What is
After studying the way such people work, we have noticed
some important themes:
Our goal is to help you become the
skilled computer user we have described above. We will
teach you a framework for problem solving with computers, (or any other type of problems!)
and help you apply that framework to various types of
application programs. We will introduce you to what
computers can do, the types of problems you may be able to
solve with specific software applications, and many
opportunities to practice with real applications on real
- These people are (generally) not super-intelligent
people who spend their whole lives with computers.
Ordinary people can learn how to control computers
with amazing flexibility and skill.
- Skilled computer users generally have a strong general
knowledge about how computers work and
what they can do. They know the main types of
applications that are used on computers, and they
know generally what features they can expect to
find within an application.
- Skilled computer users have little fear of technology.
They frequently use educated guesses to
determine how things work, and they don't worry
about being wrong once in a while. Instead, they
tend to learn from mistakes.
- Skilled computer users are often highly adaptable. They notice patterns from earlier problems, and can adapt their skills to new situations.
- The most striking characteristic of skilled computer
users is the presence of some kind of organized
problem solving strategy. Skilled computer users
are skilled problem solvers. They rely far more on
their ability to solve new problems and find answers
independently than on previous knowledge of
commands and syntax in an application program. They
are able to encounter new programs and
situations with little apprehension, because they are
confident that their problem solving ability will
help them overcome their lack of knowledge about the
We will not focus on individual software packages, although
we will certainly use them for examples and exercises. We
are less interested in actual commands and methods
for doing things, because there are so many possible paths to a correct answer. We are more interested in the process you
can use to learn how to do these things in whatever
applications you use in the future. Our goal is to teach
you the skills you will need to learn computing applications
that have not even been imagined yet!
Our most powerful tool - The STAIR steps for solving
Problem - solving can be seen as more of an art than a
science. Each person has different ways of approaching
problems. Our intention is not to limit your problem
solving processes to our way of thinking, but to give you a
framework you can fall back on when you are stuck. We have
developed a method called STAIR which has proven to be a
helpful problem - solving tool.
STAIR is an acronym. (Get used to it... computer scientists
LOVE acronyms!!) Each letter in the word STAIR represents
part of a general problem solving strategy.
- S - State the problem
- This step seems obvious enough, but it is often the
one people skip. We frequently start solving problems
before we really think carefully about what problem we are
trying to solve. The result is confusion and wasted time.
Take the time to carefully describe to yourself what you are
trying to accomplish. Avoid the temptation to couch this
problem description in technical terms. At this stage of
the process, all your thoughts should be in ENGLISH (or, of
course whatever other human language you think most
comfortably in) Some problems are best described with
sketches or other tools (like flowcharts and data diagrams)
that we will discuss later. Use whatever you need to make
sure you have a firm understanding of what you want to
accomplish. It's best to write this down on paper so you
can check it later if you start to get confused. If you
don't know where you are trying to go, how will you know
when you are there?
- T - Tools for the job
- Once we know what kind of a job we want to accomplish,
we can begin to explore which tools we might use to solve
the job. We are using the term 'tool' in a very general sense.
A tool might be a command, a button on a toolbar, a
selection on a drop - down menu, a strategy, a program, or
something else, depending on the kind of job we are trying
to do and the context within which we are working. Knowing
the capabilities of a certain program, and the kinds of
things different types of computer applications can do are
the main ways you add new tools to your toolbox of computing
skills. As you gain experience, you will constantly be
adding new tools of all kinds to your repertoire. Even the
STAIR strategy itself can be considered a tool. Most of the
time, there is more than one tool available to do a job. At
this point, just list the tools available. Later on, we
will decide which one to use. You might need to come back
to this list if it turns out you chose an inappropriate tool
the first time through the process.
- A - Algorithm development
- An algorithm is a computer science term for a
strategy or plan of action. Part of developing an algorithm
is choosing an appropriate tool or set of tools from the
previous step. The other component is determining how those
tools will be used to solve the problem. As with the other
steps, the algorithm can vary widely in the type and
complexity of the strategy you will use. In simple
problems, your algorithm may be as simple as saying "I'm
going to try pressing this particular button on the menu
bar." A more complex problem will probably require a more
complex algorithm. As before, it is a good practice to
write down your algorithm on paper.
- I - Implementation of the algorithm
- It is interesting to note that none of the steps above
require the use of a computer. The implementation step is
the actual process of translating all this human thought we
have been doing into something the computer can understand.
In simple problems, this step comes down to actually doing
a command or two. Implementation can mean "just do it" when
we are dealing with these simple problems. Programmers
think of the implementation step as translating the
algorithm into some type of computer programming language.
The process is the same regardless of the complexity of the
- R - Refinement
- We like to think that if we learn a skill and prepare
ourselves properly, we can solve a problem on the first
attempt. Experience shows us that this is usually not the
case. It is normal for a computer user to attempt a
solution several times before the problem is solved. The
first attempt at solving a problem is rarely successful. A
skilled problem solver will analyze what happened, review
the other steps, and try again. Each unsuccessful attempt
should bring you closer to an understanding of the problem
and its solution. Refinement usually means going back and
looking at the previous steps critically. Ask yourself if
you really defined the problem properly. If so, have you
used all the possible tools at your disposal? Are you sure
there is not a tool available that you have overlooked? Did
you choose the best algorithm for the job? Did you
implement the solution properly? (You would be amazed at
the number of computer errors that are the result of simple
typing or spelling errors!) Again you will find that
practice will make you much more confident at this critical
stage of the process.
Implementation of the STAIR process
As you can see, the STAIR process does provide some
guidelines for thinking about a problem, but it is not a
rigid technique. You will have to find your own variations
that work well with the way you visualize and think. Many
times you will find yourself not needing the entire process.
The STAIR convention is meant as a tool to bring out when
your natural problem solving process does not prove
sufficient. It can also be used to help you organize this
natural problem solving process.
Example One: Storing the boat
The STAIR process can be applied to situations that have
nothing to do with computing. As an example, imagine the
following situation: A man named Tom came home one day to
be confronted by his wife about the small sailboat that was
filling space in the garage. She suggested that he find a
more efficient way to store the boat than leaving it where
she normally parked her car. (Her suggestion was couched in
somewhat stronger terms than this!..) Being quite a good
problem solver, he decided to apply the STAIR methodology to
- Statement of the Problem
- Tom thinks to himself: "I need to get this boat out of
the way. It needs to go someplace where it won't be in my
wife's way, but I can still get at it easily when I want to
go sailing. I don't want to spend a lot of money or effort
on this problem, but I want a long term solution so I don't
have to deal with this again"
Notice that Tom started with as simple a statement of the
problem as possible: "I need to get this boat out of the way." He also listed some of the relevant
constraints. He didn't worry about exactly what the
solution might be yet. This may not be the finished
statement of the problem. Tom may find that he needs to
come back and refine his problem statement a little more
before he can find a solution.
- Tools Available
- Tom thinks: "This job might require actual physical
hand tools, and I've got a pretty good set of the standard
tools. Besides the obvious definition of the word tool, I
might think of some of the main approaches to solving the
problem as tools. I could hang the boat from the ceiling of
the garage, attach it to the walls, put it in the yard, or
rent some storage space."
Notice how flexible he was with the term `tool.' This
approach allows Tom to think of the IDEAS he will choose
from, as well as the physical entities. In fact, the actual
mechanical tools that will be used will be decided much
later in the problem solving process. It's way too early to
worry about whether he will use a hammer or a screwdriver. Eventually, however, Tom will have identified a smaller part of the job (How do I attach this hook to the ceiling?) that will require its own tool selection process. He may have a hook ready to go and wonder how he will attach it to the ceiling. This is where he might look at his physical tools and choose one from the box.
- Tom thinks: "I'll try hanging the boat from the
ceiling. This seems like the best approach, because the
boat will be ugly in the yard, I can't afford rental space,
and the walls are already full. I think the boat is light
enough to be suspended from the ceiling safely with some
In this instance, the algorithm step involved choosing the
best alternative from the tools step. At this point, he had
made a decision about how he was going to tackle the
problem. Notice that he also started thinking about which
physical tools (in this case a rope) he would use to help
solve the problem.
- Tom says to himself: "When the time came to actually
suspend the boat, I quickly realized I had more to think
about. I measured the ceiling and found a perfect spot, and
I moved the boat to the floor directly under the spot, but I
didn't know how exactly to attach the boat to the ceiling.
The ceiling has wooden rafters in it. I obviously need to
attach some sort of hooks to the rafters. I also noticed
that the rope I planned to use was kind of slippery and
might not hold a knot very well. "
The implementation step so far has been unsuccessful in the
obvious sense; the boat is still sitting on the garage
floor. Rather than being discouraged by this, Tom will use
the experience as an information gathering stage for the
- R Refinement
- Tom thinks: "The ceiling idea is still a good one, but
I don't have everything I need. I don't trust this rope,
and I need some hooks or something. Digging through the
toolbox, I found one bicycle hook that will work fine for
the bow of the boat. I can attach that to a rafter easily,
but I still need to hold up the back end of the boat. I
noticed the straps I use to carry the boat on top of my car.
They are plenty strong enough, but the ends of the straps
are designed to fit in the rain gutter of my car. I need to
find something that will allow me to attach the straps
securely to the rafters. I went to the hardware store and
found screen door handles! They will attach to the rafters
and they are the perfect size to attach the straps to! I
went back home, attached the handles, hoisted the boat up in
the straps, and the problem is solved!"
During the refinement step, Tom made some visits back to many of the
other parts of the problem solving process. He
had to adjust his perception of the problem. Attaching the
boat to the ceiling was a good idea, but Tom's first
statement of the problem did not specify how he was going to
do this. Finding a way to solve this part of the problem
involved combining algorithm development and tool selection.
The implementation happened in segments as he found more of
the right ideas and tools to solve the problem. The process
does not always flow in a set order, but because he used a
systematic approach, he always knew how to think about
solving the problem. Tom knew, for example, that his
algorithm was good, but that he would need to rethink his
tool selection. Obviously, plenty of people solve this kind
of problem without ever taking a computer science class.
Tom may not even know that he was using an organized problem
solving technique. The reason that we start with this
problem is to illustrate that our problem solving process is
really just a somewhat formalized summary of the techniques
we already recognize as problem solving techniques in many
Example Two - Drawing a map
- Statement of the Problem
- Nancy has moved to a new town. Her aunt wants to come
visit her. Nancy wants to use her new computer to draw a
map from her aunt's home to her new house. She decided to
use the computer so she can easily make copies to send to
other friends later.
- Tools available
- Nancy thinks carefully about the tools she needs. She
knows her computer has a drawing program already installed, but she
has never used the program. She does know how to get to the
program and start it up
- Nancy starts by sketching out the map with a pencil on
paper. Now she knows the image she wants to create. She
will use lines to note streets, squares for specific
landmarks, and text to label the streets and landmarks.
When she has finished with the picture, she will save it to
her disk in case she needs it again, and print it out to
include in her next letter.
- Nancy stares at the blank screen. She doesn't know
what to do next. She knows by examining her algorithm that she has a number of new
- She needs to draw some rectangles
- She needs to draw some lines
- She needs to place some text on the picture
- She needs to save the picture somehow
- She needs to print the picture somehow
Nancy has a dim recollection of the STAIR process from a
computer class in her past. She wonders if she
should apply that process to one of the littler problems now.
She decides to start with the rectangles
- Statement of problem: Nancy needs to draw a
rectangle to represent her Aunt's house
- Tools: She spots a button on the toolbar that has a
picture of a rectangle! If that doesn't work,
she knows she can cruise the menus for a likely -
looking command, or check the on-line help.
- Algorithm: She decides "What the heck. I'll press
it and see what happens."
- Implementation: She presses the button. The cursor
on this screen changes, and when she drags the
mouse on the screen, she is able to draw a
rectangle. She practices a few times until she has the hang
- Refinement: After she knows how to make a rectangle
exactly how she wants, she puts one where
her aunt's house should be on the map.
- R - Refinement
- Nancy repeats the process to learn the other tools
she might need. Most of the things she needed relate
directly to buttons on the toolbar. She does not see a
button that might represent printing. She looks in the on-
line help and finds that Print is an option in the File
menu. She then looks at the menu and finds the command.
She uses it and the picture shows up in her
printer. Problem solved!
Analysis of Nancy's experience
Notice that the problem solving process actually had to
occur at two distinct levels in this project. First, Nancy
had to think about the big picture of how to draw the map.
As a part of this big problem, she discovered a number of
smaller problems along the way. She applied the same kind
of process to the smaller problems and was able to learn
many new skills as part of solving the larger problem. The
next time she needs to use this graphics program, she will
already know how to use these particular tools without
having to relearn them. In fact, if she tries ANY graphics
program, she will have a head start, because she already
knows to expect some kind of line drawing tool, rectangle
tool, and other tools that she learned to use in this
Today in lab you will use special computer program designed to introduce you to the most basic computer skills. You will practice using the keyboard, editing text, locating special keys, using the mouse, using drop down menus, and accessing on - line help. After you finish the program, you will get to play some games. The lab instructor will NOT tell you how to play the games. It is up to you to figure out how the games work and how to play them. Use the STAIR technique to figure out how each game works. The lab instructor will demonstrate how to start the program.
Vocabulary / Main Concepts
- Computers are universal machines - the same machine can do many different kinds of tasks
- A computer is most effectively thought of as a problem solving tool rather than as a traditional machine
- Learning to use computers effectively requires problem solving ability
- The STAIR method is one way of organizing the problem solving process
- Statement of Problem: defining with words, sketches, or other means what you want to accomplish
- Tools: Concepts, Commands, Menu items, Toolbar buttons, programs, or ideas that can help you
solve a problem
- Algorithm: A strategy for solving a problem
- Refinement: The process of studying an unsuccessful attempt at problem solving and looking back at
earlier steps to approach a solution
The way we learn about using most machines is not adequate when we are trying to learn how to use a computer. Problem solving ability is a major factor in success with computers. The STAIR technique for problem solving is a good way to summarize the problem solving process. Problem solving is a fluid process. It may be necessary to apply the process to a large problem, to break that problem into many smaller problems, and apply the same process to the smaller problems.
- Why is the way we learn to use typical machines insufficient when we are learning to use computers?
- What thinking skill best summarizes skilled computer users?
- Write out the steps for the STAIR method.
- Write a one sentence summary of each step of the STAIR method.
- Thnk of the way you already solve non - computing problems:
- Do you have some type of systematic technique for solving problems?
- What do you do when you are stuck?
- Can you see some relationship between your current technique and the STAIR method?
- Imagine that your friend calls you and tells you a skunk has gotten into his basement. Use the STAIR
method to summarize how you will 'de-skunk' the basement.
- Think of a problem you solved recently. Describe how you solved the problem in terms of the
STAIR method. Write down how your thinking fit with the STAIR steps.
- As you learn one of the games in today's lab, try to apply the STAIR technique to learning how to
play the game. Write down the steps of the STAIR method, and how you used each part of the
process to learn the game.
Module Effectiveness Assessment / questions for the committee
- Does early emphasis on problem solving make development of other modules easier?
- Can students apply it on non - computer problems such as the review questions?
- Can they apply it in the lab when learning the games?
- Should we have approached this module using a STAIR organization?
- Is the organization sufficient?
- Is this the appropriate tone, writing style, audience level?
- Is html the correct format for sharing this information?
- How do we deal with authorship, copyright issues?
(c)1996, Andy Harris,
IU System-wide Course A/B Development