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CISC 108: Introduction to Computer Science I, Fall 2014! Lab 2
Lab 2!
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Goals!!
Relevant sections of HtDP/2e: Chapters 1, 2, and 3 and Chapter 4 Sections 1.
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This week’s lab will help you to practice:
• conditionals, intervals, enumerations
• function composition: writing more complex functions by combining simpler
functions
• using the design recipe!
• simple interactive programming using the universe library
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Note: Exchange email addresses and phone numbers with your partner. Decide on
your next meeting time this week in case you don’t finish. Make sure both names are
at the top of your lab submission!
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Batch Program Problems!!
Note: Follow the Design Recipe! For each problem, consider if you need a Data
Definition more precise than just Number, String, Boolean, or Image. What is the
function Signature? The Purpose? Write at least one Example / Unit Test for every
different kind of data consumed and produced. Create the function Header with a body
stub that is an atomic value of the correct output type. Only now do you need to
consider how to actually write the function body (and if the inputs are enumerations,
then the body should say, case-by-case, what to do for each possible value using
cond). Don’t be scared of a blank Definitions Window, and be aware that we grade
each of these steps separately.
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Problem 1: Body Mass Index (BMI) is a number calculated from a person’s weight and
height that is a fairly reliable indicator of body fatness for most people. [http://
www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html]
Design a function bmi that consumes a person’s weight in pounds and height in inches,
and computes that person’s BMI. Make sure to document your intended interpretation
of the function parameters.
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http://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html
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CISC 108: Introduction to Computer Science I, Fall 2014! Lab 2
Follow the Design Recipe! We expect EVERY function you write, from now on, with few exceptions,
to include the signature, purpose statement, and examples turned into unit tests, in addition to the
necessary function header and body.
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Problem 2: For adults 20 years old and older, BMI is interpreted using standard weight
status categories that are the same for all ages and for both men and women. For
children and teens, on the other hand, the interpretation of BMI is both age- and sex-
specific. The standard weight status categories are underweight, normal, overweight,
and obese. Write a data definition for WeightStatusCat as an enumeration.
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Problem 3: The standard weight status categories associated with BMI ranges for
adults are shown in the following table:
Design a function bmi.>wvc to convert a BMI value to a standard weight value
category.
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Problem 4: The Psychology department has purchased a sign to advertise how many
students are needed for experiments today. The sign has a keypad to enter a number,
but the actual text displayed on the sign must be programmed using a function that
consumes a number and produces a string to display.
Unfortunately, the first version of the code has a problem. It works fine for any positive
integer, or even 0 except for the number 1:
2 students are needed for experiments
22 students are needed for experiments
0 students are needed for experiments
1 students are needed for experiments !
They would prefer it say “1 student is needed for experiments”. Design the function
psych.sign to consume a non-negative integer and produce the correct string.
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BMI Weight Status
Below 18.5 Underweight
18.5 up to but not including 25 Normal
25 up to but not including 30 Overweight
30 and above Obese
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CISC 108: Introduction to Computer Science I, Fall 2014! Lab 2
Problem 5: The local student chapter of the Association for Computing Machinery (one
professional organization for computer scientists) really likes your sign, and asks for
one customized for them. Design a function acm.sign that also consumes a non-
negative integer, but produces either “n students join the ACM” or “1 student joins the
ACM”.
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Problem 6: Abstraction. You are now getting 10 sign requests every day. You decide to
write one program to handle all of these signs, and even some you haven’t thought of
yet. You look at your examples for patterns (we’ve added space just to make it more
obvious):
2 students are needed for experiments
1 student is needed for experiments
22 students join the ACM
1 student joins the ACM
12 buses are leaving now
1 bus is leaving now
5 burgers are ready to eat
1 burger is ready to eat
16 fish are free with any purchase
1 fish is free with any purchase !!
The pattern you discover is:
You initially consider designing a function that consumes a number, singular noun,
plural noun, singular verb, plural verb, and the verb phrase, but realize that most of the
time you can figure out the plural form of the noun and the verb given only the singular
form, and the irregular cases you can handle as extra clauses in a conditional
statement.
Because one of the most basic Rules of Program Design is
“One Task, One Function, One Purpose”
and we have three tasks (pluralizing the nouns, pluralizing the verbs, and putting the
whole sign together either with or without plurals), we will therefore design three
functions.
• (6a) Design a function any.sign that consumes a non-negative integer, a singular
noun string, a singular verb string, and a verb phrase string and produces the
appropriate correct English output string depending on the value of the integer (1
means singular, and anything else is plural). This function should work for all the
examples above, and call the following two helper functions.
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CISC 108: Introduction to Computer Science I, Fall 2014! Lab 2
• (6b) Design a function pluralize.noun that consumes a singular noun string and
produces the plural. It should work for regular nouns (add an “s” at the end),
regular nouns that end in “s” (add “es”), and the special cases “fish” and “deer”
that are their own plurals. Note that new special cases can be added easily. Feel
free to use functions you wrote for lab 1.
• (6c) Design a function pluralize.verb that consumes a singular verb string and
produces the plural. It should work for regular verbs (remove the trailing “s”) and
the irregular verb “is” (plural “are”).
When you have Problem 6 working, it is Best Practice to refactor [rewrite] your
solutions for Problems 4 and 5 to use your new more abstract function: comment out
your old definitions for Problems 4 and 5, and replace them with new definitions that
call only our new, more general solution, any.sign.!
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Interactive Program Problem!!
Let’s actually build the Psychology dept. sign using the Universe package. An
interactive program consists of several parts: an underlying computational model of
the world, a mapping from that model to a view that people can see (here, a graphical
view), and controllers that interact with people (or other things, like the computer’s
clock) to change the model.
At this point our model can only be a simple piece of atomic data (wait until next week!)
or simple itemization. The model must represent what changes; what the user
manipulates. Here, that will be the number of students needed today. The number of
students needed gives us the information to create a view, and the user can use the
number keys to change the number displayed.
Interactive programs are created using the big-bang form, which in turn requires us to
write several different functions with pre-specified signatures. We’ll take these one at a
time.
For this section, we use the following Data Definition (copy into your solution file):
;; a PSWorld [Psych Student World] is a Non-Negative Integer,
;; representing the number of students we need today for experiments !
Problem 7: Design the function draw.psych.sign that consumes a PSWorld and
produces an Image of the psych.sign string (read that twice: consumes a PSWorld<
and produces an
If you load your definitions and call, for example, (main<5), you should get the correct
sign. Now to add some interaction using the keyboard.
When you press a key, a key-event is generated by the keyboard controller that can
be used to “change” the world (the model). For example, we could set it up that
pressing “1” changes the number of students to 1, pressing “7” changes it to 7, and so
on for all 10 single digit keys. Note that the key controller effects only the model, not
the view (you already wrote a function that draws whatever the current model is on the
screen: the model and the view are separate)!
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Problem 8: Design a function handle.key that consumes a PSWorld and a KeyEvent,
and produces a new PSWorld representing the new number of students (forgetting
whatever the number was beforehand). So for example
(check-expect (handle-key 5 “8”) 8)
(check-expect (handle-key 5 “g”) 5) ;ignore anything not a digit !
Note that you should compare keys using (key=?
(on-key handle-key))) ;PSWorld KeyEvent —-> PSWorld !
Now if you run (main<5) in the interactions window, you should be able to change the
number in the display by typing keys.
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Problem 9: Redesign handle.key so that the up arrow (key event “up”) adds one to
the current PSWorld, and the down arrow (key event “down”) subtracts one.
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Problem 10: Redesign handle-key so that if we type multiple numbers in a row we get
larger numbers: that is, typing 435 would give a display “435 students are needed for
experiments”. Hint: if our world is 0 and we type 3, the new world is 3. If the world is 3
and we type 4, the new world is 34. If the world is 34 and we type 9, the new world is
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CISC 108: Introduction to Computer Science I, Fall 2014! Lab 2
349, etc. the new world is 10 times the old world plus the key typed. Add a clause that
typing the space bar (key event “ “) sets the world back to 0.
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Problem 11: look up in the help desk how to add support for the mouse controller.
You will need to design a handle.mouse function, and add (on.mouse