CS Homework 2 p. 1. CS Homework 2

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1 CS Homework 2 p. 1 Deadline 11:59 pm on Friday, February 2, 2018 Purpose CS Homework 2 To practice defining and using named constants and check-expect expressions, and to practice using the design recipe to define and test functions. How to submit You will submit your 111hw2.rkt file for Homework 2 on the course Canvas site. Each time you would like to submit your work so far: Save your current DrRacket Definitions window contents in a file with the name 111hw2.rkt Note: please use that exact name -- do not change the case, add blanks, etc. If I search for a file with that name in your submission, I want it to show up! Open a web page to connect to Click on the icon for the CS 111 course, then choose the Homework 2 link (in the Homeworks section). Follow the Canvas instructions for uploading your Racket file 111hw2.rkt. Important notes Signature and purpose statement comments are ONLY required for functions that you have written and defined yourself you do not write them for named constants, or for functions that are already built into the Racket environment or the teachpacks. Remember: A signature in Racket is written as a comment, and it includes the name of the function, the Racket data types of expressions it expects in the order they're to be expected, and the Racket data type of the expression it produces. This should be written as discussed in class. For example, signature: triple: number -> number signature: say-bye: string -> string signature: avg-trio: number number number -> number signature: purple-star: number -> image Remember: a purpose statement in Racket is written as a comment, and it describes what the function expects and describes what the function produces (and if the function has side-effects, it also describes those side-effects). For example, purpose: expects a number, and produces triple that number purpose: expects a name, and produces the string containing "Goodbye, " followed by their name purpose: expects three numbers, and produces the average of those three numbers purpose: expects a size in pixels (which is the distance between

2 CS Homework 2 p. 2 points of a 5-pointed-star), and produces an image of a solid purple star of that size Remember: it is a COURSE STYLE STANDARD that named constants are to be descriptive and written in all-uppercase -- for example, (define WIDTH 300) it is ANOTHER course style standard that parameters and function names are to be descriptive and written in all-lowercase -- for example, (define (triple num)...) You should use blank lines to separate your answers for the different parts of the homework problems. If you would like to add comments noting which part each answer is for, that is fine, too! The design recipe is important! You will receive substantial credit for the signature, purpose, header, and examples/check-expects portions of your functions. Typically you'll get at least half-credit for a correct signature, purpose, header, and examples/check-expects, even if your function body is not correct (and, you'll typically lose at least half-credit if you omit these or do them poorly, even if your function body is correct). Problem 1 NOTE: you are NOT writing any new functions in this problem -- you are practicing writing and using a named constant, and practicing writing some check-expect compound expressions. Open a new Racket Definitions file (it's a good idea to immediately save the file in the folder where you want your Racket file to go, and save often as you go!) and type in comments at the beginning of the file, containing: a comment-line containing your name, followed by a comment-line containing CS HW 2, followed by a comment-line giving the date you last modified this homework -- for example: type in YOUR name CS HW 2 last modified: Then put a blank line, and the expression that loads the 2htdp/image teachpack. Blank lines help make your code more readable! (require 2htdp/image) Below this, after a blank line, now type the comment lines: Problem 1 1 part a Remember the image you created for Homework 1, Problem 6? Copy that compound expression here. (If you didn't finish Homework 1, Problem 6, then create a new compound expression from those instructions.) You are probably more familiar now with image operations than you were when completing Homework 1 --

3 CS Homework 2 p. 3 as long as the image still meets the requirements from Homework 1, you may change and improve upon the image if you would like to. This is optional. Here, again, are the requirements for the image: ******** FROM HOMEWORK 1, Problem 6 ******** Write one or more expressions that meet the following requirements: the final resulting image somehow should be the result of at least THREE different image or imagerelated operations from the 2htdp/image teachpack. (More is fine!) They can be image operations from the "Some DrRacket Tidbits" handout, OR they can be image operations (from the 2htdp/image teachpack) that you find by exploring DrRacket's Help feature, described a bit at the end of the "Some DrRacket Tidbits" handout. the final resulting image should be an expression of type image that is precisely 200 pixels wide and 200 pixels high ACCEPTABLE "extended" version of this problem: IF you would like to use define to give names to some expressions to make your task easier, that is allowed and encouraged (but not required) for this problem. [We had not yet covered the style rules for such named constants for Homework 1 -- since we have now, make sure any such named constants are now descriptive and written in all-uppercase.] As long as you meet the above requirements, your image may be as simple or as complex as you would like. ******** end of part FROM HOMEWORK 1, Problem 6 ******** THEN: write a Racket define expression to define a named constant whose value is your entire finished image. write the simple expression consisting of your newly-defined named constant -- when you now click Run, you'll see that the value of this named constant is your image. 1 part b You're now going to test that your image is exactly 200 pixels wide and 200 pixels high. Recall that operation image-width expects an image and returns its width in pixels, and that operation image-height expects an image and returns its height in pixels. Write TWO check-expect expressions: Write a check-expect expression, using image-width and the named constant for your finished image from Problem 1a, that will pass if your named constant image is exactly 200 pixels wide. Write a check-expect expression using image-height and the named constant for your finished image from Problem 1a, that will pass if your named constant image is exactly 200 pixels high. Run your code to test your image! If your image doesn't pass both tests, then you need to revisit Problem 1 part a and alter your image so that it passes the tests. Problem 2

4 CS Homework 2 p. 4 Problem 2 Now, you are defining a new function! First, consider: given a rectangle's measurements, how can you figure out that rectangle's perimeter (the distance AROUND that rectangle)? You are now going to follow the design recipe steps to write a function rect-perim (I'm specifying the function name to make it easier to test when the assignments are graded). 2 part a How many and what data type of expression(s) should rect-perim expect, to be able to return such a perimeter? What data type should rect-perim produce? Now write an appropriate signature comment for rect-perim. 2 part b Write an appropriate purpose statement comment for rect-perim. 2 part c START the define expression for the function rect-perim, including an appropriate function header 2 part d Write at least 2 specific tests/check-expect expressions for rect-perim. Interestingly, you may actually place these either before or after your not-yet-completed function definition, whichever you prefer. 2 part e Only NOW should you replace the... in rect-perim's function body with an appropriate expression to complete this function, that calculates the value rect-perim will produce. Run and test your function rect-perim until you are satisfied that it passes its tests and works correctly. Finally, write at least 2 expressions of your choice that run your function rect-perim (so that you will see their results) after your function definition for rect-perim. Problem 3 Problem 3

5 CS Homework 2 p. 5 Consider a function that asks a given person how their day is going. Given a person's name, it returns How's it going,...that person's name...? (Optionally, you may change the exact wording of the question, as long as it includes the person's name and ends with at least one question mark.) You are now going to follow the design recipe steps to write this function ask-abt-day. 3 part a How many and what data type of expression(s) should ask-abt-day expect, to be able to return such a question? What data type should ask-abt-day produce? Now write an appropriate signature comment for ask-abt-day. 3 part b Write an appropriate purpose statement comment for this function. 3 part c START the define expression for the function ask-abt-day, including an appropriate function header 3 part d Write at least 2 specific tests/check-expect expressions for ask-abt-day, placed either before or after your not-yet-completed function definition, whichever you prefer. 3 part e Only NOW should you replace the... in ask-abt-day's function body with an appropriate expression to complete this function, that determines the value ask-abt-day will produce. Run and test your function ask-abt-day until you are satisfied that it passes its tests and works correctly. Finally, write at least 2 expressions of your choice that run your function ask-abt-day (so that you will see their results) after your function definition for ask-abt-day. Problem 4 Problem 4 Suppose someone decides it would be useful to be able to take an image and its desired title, and create a new image that includes that image above that title (as PART of the resulting image), with the title shown in 24- pixel-high black letters. You are now going to follow the design recipe steps to write this function title-img. (HINT: The text function expects a string and produces an image from the contents of the string.)

6 CS Homework 2 p. 6 4 part a How many and what data type of expression(s) should title-img expect, to be able to return such an image? What data type should title-img produce? Now write an appropriate signature comment for title-img. 4 part b Write an appropriate purpose statement comment for this function. 4 part c START the define expression for this function title-img, including an appropriate function header 4 part d Write at least 2 specific tests/check-expect expressions for title-img, placed either before or after your not-yet-completed function definition, whichever you prefer. 4 part e Only NOW should you replace the... in title-img's function body with an appropriate expression to complete this function, that determines the value title-img will produce. Run and test your function title-img until you are satisfied that it passes its tests and works correctly. Finally, write at least 2 expressions of your choice that run your function title-img (so that you will see their results) after your function definition for title-img. Problem 5 Problem 5 Consider a function total-feet that expects a number of yards and a number of feet, and returns the total number of feet. (For example, the value of the expression (total-feet 4 5) should be 17, because 4 yards and 5 feet is 17 feet overall.) You are now going to follow the design recipe steps to write this function total-feet. 5 part a This part comes BEFORE starting the function total-feet! FIRST: write a Racket definition for a named constant that will define the name FEET-PER-YARD to be the number of feet in a yard. (FEET-PER-YARD is NOT a function! It is just a number, the number of feet in a single yard.)

7 CS Homework 2 p. 7 5 part b How many and what data type of expression(s) should total-feet expect from the user, to be able to return such a total? What data type should total-feet produce? Now write an appropriate signature comment for total-feet. 5 part c Write an appropriate purpose statement comment for total-feet. 5 part d START the define expression for this function total-feet, including an appropriate function header 5 part e Write at least 2 specific tests/check-expect expressions for total-feet, at least one for a number of yards of 0, and at least one for a number of yards greater than 1, (each with a DIFFERENT number of feet),...placed either before or after your not-yet-completed function definition, whichever you prefer. 5 part f Only NOW should you replace the... in total-feet's function body with an appropriate expression to complete this function, that determines the value total-feet will produce. FOR FULL CREDIT, ALSO make sure that you USE the named constant FEET-PER-YARD appropriately within total-feet's function body's expression. Run and test your function total-feet until you are satisfied that it passes its tests and works correctly. Finally, write at least 2 expressions of your choice that run your function total-feet (so that you will see their results) after your function definition for total-feet. Problem 6 Problem 6 (This is adapted from Homework 1 of J. Marshall's "The Way of the Program" course at Sarah Lawrence College.) The Tasty-Waking coffee roasters sells whole-bean coffee at $6.95 per pound plus the cost of shipping. Each order ships for $0.75 per pound plus $2.75 fixed cost for overhead.

8 CS Homework 2 p. 8 (For example, if someone buys 1 pound of whole-bean coffee, the total price is $ If someone buys 2 pounds of whole-bean coffee, the total price is $ If someone buys 5 pounds, the total is $41.25.) 6 part a FIRST: The description above includes 3 constant values. Define 3 appropriate, descriptive named constants for these values. (This is so, when prices change, all you need to do is change the constant definitions!) 6 part b Consider a function named order-cost whose purpose is to calculate the total cost for an order. How many and what data type of expression(s) should order-cost expect from the user, to be able to return such a total cost? What data type should order-cost produce? Now write an appropriate signature comment for order-cost. Hint: don't include named constants in the signature! The 3 named constants do NOT need to be given as arguments to this function! Think about it this way a customer doesn't need to tell you the prices of your product and shipping costs you already know that because you work there and are already aware of those prices. The value(s) the function should expect is/are the value(s) a customer does need to give when placing an order. So what does a customer need to tell the store when ordering coffee beans? 6 part c Write an appropriate purpose statement comment for order-cost. 6 part d START the define expression for this function order-cost, including an appropriate function header (Hint: named constants do not belong in a function header, either your function header should have parameter identifiers only for what the signature and purpose say is expected by the function.) 6 part e Write at least 2 specific tests/check-expect expressions for order-cost, placed either before or after your not-yet-completed function definition, whichever you prefer. 6 part f Only NOW should you replace the... in order-cost's function body with an appropriate expression to complete this function, that determines the value order-cost will produce. FOR FULL CREDIT, ALSO make sure that NOW you USE the named constants from Problem 6 part a ppropriately within order-cost's function body's expression. Run and test your function order-cost until you are satisfied that it passes its tests and works correctly. Finally, write at least 2 expressions of your choice that run your function order-cost (so that you will see their results) after your function definition for order-cost.