CIS 252 Introduction to Computer Science Exam 1 (Green) October 3, Points Possible

Transcription

1 Name: CIS 252 Introduction to Computer Science October 3, 2018 Question Points Possible Points Received Total 100 Instructions: 1. This exam is a closed-book (and closed-notes) exam. 2. Legibility counts! Make sure we can read (and find!) your answers. If you need more room for an answer than that given, use the back side of the pages. Be sure to leave a note indicating where the answer is. 3. This test should have 8 pages (including this cover sheet). Let us know now if your copy does not have the correct number of pages. 4. Unless specified otherwise, you may use any built-in Haskell function you want, as long as you use it correctly (including using its correct name). The last page includes a list of some common Haskell functions and their types.

2 1. (34 points) Suppose that the following definitions are made: import Data.Char zamboni :: [Float] zamboni = [10.0, 12.2, 48.6, 15.3, 63.7] pads :: [Int] pads = [ 2*x x <- [4,5,7,2,1], odd x ] zone :: (Int,Char) -> Bool zone (k,ch) = isupper ch && even k dangle :: [a] -> Float -> Float dangle (x:y:rest) n = 3 + dangle rest n dangle _ n = n score :: Integer -> Bool -> Integer score q line line q > 7 = 31 otherwise = q celly :: a -> Integer -> [a] celly s w w > 25 = [s,s] otherwise = [] skate :: a -> [a] -> [a] skate ch [] = [ch] skate ch (c:cs) = c : ch : skate ch cs (a) (22 points) Give the values of the following expressions. (i). 4 /= 2*3 (ii). [3,9]:[] (iii). length [[6,2],[8],[],[1,0,4],[9]] (iv). pads (v). zone (5, A ) (vi). mod (vii). skate 2 [7,3,6]

3 (viii). [2,7..14] (ix). dangle [2,4,8,3,7] 500 (x). zip [57, 48] [16,81,25,4] (xi). score 6 True (b) (12 points) Give the types of the following expressions (e.g., the type of [False] is [Bool]). (i). (even 21, K ) (ii). [pads, pads, pads] (iii). score 35 True (iv). celly "goal" 3.7 (v). [ dangle [w] 3.1 w <- pads ] (vi). zip pads zamboni import Data.Char zamboni :: [Float] zamboni = [10.0, 12.2, 48.6, 15.3, 63.7] pads :: [Int] pads = [ 2*x x <- [4,5,7,2,1], odd x ] zone :: (Int,Char) -> Bool zone (k,ch) = isupper ch && even k dangle :: [a] -> Float -> Float dangle (x:y:rest) n = 3 + dangle rest n dangle _ n = n score :: Integer -> Bool -> Integer score q line line q > 7 = 31 otherwise = q celly :: a -> Integer -> [a] celly s w w > 25 = [s,s] otherwise = [] skate :: a -> [a] -> [a] skate ch [] = [ch] skate ch (c:cs) = c : ch : skate ch cs

4 2. (16 points) Consider the following (partial) file system hierarchy, where the numeric labels associated with directories are intended merely as identification for the questions that follow: 1 / firstorder/ droids/ planets/ resistance/ kylo/ snoke/ crait/ jakku/ rey/ finn/ tico/ poe/ books/ droids/ falcon/ For each question that follows, suppose that Rey s home directory is directory #10 and that her current working directory is directory #6. (a) If Rey executed the Unix command pwd, what would be the system s response? (b) If Rey executed the Unix command cd.., which directory would become her current working directory? (Give the number of the directory, not the name.) (c) If Rey executed the Unix command cd ~/droids, which directory would become her current working directory? (Give the number of the directory, not the name.) (continued on next page)

5 As before, suppose that Rey s home directory is directory #10 and that her current working directory is directory #6. For each of the following tasks, give a single Unix command would allow Rey to complete the task. You should assume that each task is completed independently of the others (i.e., changes made in one task do not affect other tasks). (d) Make a copy of the file helmet.txt (located in directory #9), placing it in directory #16 with the name gear.txt (e) Create a subdirectory in directory #11 called health (f) Delete the file rocks.pdf (located in directory #8) (g) Get a long listing (e.g., info about file permissions and creation dates) for directory #7, but do not include hidden files (h) Move the file bb8.hs (located in directory #15) to directory #13 1 / firstorder/ droids/ planets/ resistance/ kylo/ snoke/ crait/ jakku/ rey/ finn/ tico/ poe/ books/ droids/ falcon/

6 3. (18 points) A small local village has recently changed how they calculate the cost of speeding tickets. The new costs are computed as follows: The cost of driving at or below the speed limit is 0. (That is, there is no penalty for those who don t exceed the speed limit.) Driving above the limit at a speed higher than 130 miles per hour (mph) always results in a $2500 ticket. For driving speeds at or under 130 mph, each of the first 15 mph over the speed limit costs $50 each, and each subsequent mph over the speed limit costs $75. The following examples illustrate how these rules are applied: Suppose that the speed limit is 65 mph. Driving 64mph costs nothing, driving 67mph costs $100 (= 2 $50), driving 83mph costs $975 (= 15 $ $75), and driving 135mph costs $2500. Suppose that the speed limit is 25 mph. Driving 64mph costs $2550 (15 $ $75), whereas driving 135 mph costs $2500. (Yes, it seems outrageous that a person driving at 64mph pays more than someone driving at 135mph, but that s how the stated rules work. Perhaps the village council should have thought things out more carefully.) Write a Haskell function ticketcost :: Integer -> Integer -> Integer such that ticketcost limit speed computes the cost of a speeding ticket for driving speed miles per hour (mph) in a zone that has the speed limit limit (in mph). In writing your function, you may assume that speed and limit are never negative (i.e., your function does not need to check for those cases). For example, the function should have the following behavior: *Main> ticketcost *Main> ticketcost *Main> ticketcost *Main> ticketcost *Main> ticketcost

7 4. (10 points) Write a Haskell function addevens :: Integer -> Integer -> Integer such that addevens k n computes the sum of all of the even numbers from k up to n (inclusive). Note that k may be odd or even, and n may be odd or even; if k is greater than n, your function should return 0. For example, the function should have the following behavior: *Main> addevens = *Main> addevens = *Main> addevens because 12 > 7 0 *Main> addevens because there are no evens between 7 and (10 points) Write a Haskell function allpos :: [(Char,Integer)] -> Bool such that allpos ps returns True if every pair in ps contains a positive integer, and it returns False if at least one pair contains a nonpositive integer. For example, the function should have the following behavior: *Main> allpos [( a,3), ( b,1), ( g,7), ( a,1), ( w,2)] True *Main> allpos [( a,3), ( b,-6), ( g,7), ( a,1), ( w,2)] False *Main> allpos [] True

8 6. (12 points) Write a Haskell function dropcaps :: String -> String such that dropcaps cs returns the list obtained by removing the longest possible prefix of cs that contains only uppercase letters. For example, dropcaps "ABCdeFGhij" returns "defghij" (i.e., all of the uppercase letters at the front of the string were removed), and dropcaps "25WabXY" returns "25WabXY" (i.e., there were no uppercase letters at the front of the string). Types of some standard Haskell functions (:) :: a -> [a] -> [a] (++) :: [a] -> [a] -> [a] (&&), ( ) :: Bool -> Bool -> Bool even, odd :: Integral a => a -> Bool length :: [a] -> Int isalpha, isupper, islower :: Char -> Bool toupper, tolower :: Char -> Char zip :: [a] -> [b] -> [(a,b)]