CS 190 Exam 2 Fall 2014

Transcription

1 CS 190 Exam 2 Fall 2014 Name (print): Instructions: Keep your eyes on your own paper and do your best to prevent anyone else from seeing your work. Do NOT communicate with anyone other than the professor/proctor for ANY reason in ANY language in ANY manner. This exam is closed notes, closed books, and no calculator. Turn all mobile devices off and put them away now. You cannot have them on your desk. Write neatly and clearly indicate your answers. What I cannot read, I will assume to be incorrect. Stop writing when told to do so at the end of the exam. I will take 5 points off your exam if I have to tell you multiple times. Academic misconduct will not be tolerated. Suspected academic misconduct will be immediately referred to the Emory Honor Council. Penalties for misconduct will be a zero on this exam, an F grade in the course, and/or other disciplinary action that may be applied by the Emory Honor Council. Time: This exam has 7 questions on 12 pages including the title page. Please check to make sure all pages are included. You will have 75 minutes to complete this exam. I commit to uphold the ideals of honor and integrity by refusing to betray the trust bestowed upon me as a member of the Emory community. I have also read and understand the requirements and policies outlined above. Signature: Question: Total Points: Score: 1

2 1. Answer the following questions briefly. You do not need a formal definition, just a clear answer. You may use a code example if it would be helpful. (a) (2 points) What is the difference between print and return statements? Solution: print: pg return: pg 99 (b) (2 points) What is a boolean expression? Solution: An expression(combination of variables, values, and operators) which evaluates to either of the values True or False. The most common ways to generate boolean expressions we have studied are with the use of comparison (>, <, >=, >=,!=, ==) and logical (and, or, not) operators. (c) (2 points) What is an infinite loop? Solution: A loop which never ends. E.g. x = 1 while x < 5: print(x) (d) (2 points) What is the difference between the = and == operators? Solution: = is the assignment operator. E.g. x = 2 assigns the value 2 to the variable x. == is the equality operator. E.g. x == 2 returns True/False and tests whether the value of the variable x is equal to the value 2. (e) (2 points) List two different sensors on your robot. Solution: brightness/getbright, light/getlight, camera, IR/getIR, obstacle/getobstacle... 2

3 2. For each of the following snippets of code, indicate what would be printed/displayed to the screen. (a) (4 points) x = 1 while x < 5: print( x+1 ) x = x + 1 Solution: 2, 3, 4, 5 (on separate lines) (b) (6 points) for n in range(1,9): if (n%3 == 0) or (n%5 == 0): print(n, "oak") elif (n%4 == 0): print(n, "elm") if (n==5): print(n, "birch") Solution: 3 oak 4 elm 5 oak 5 birch 6 oak 8 elm (c) (2 points) def fastfurious(movienum): if movienum > 8: print("not yet made") return print("fast Cars!") fastfurious(9) Solution: Not yet made 3

4 (d) (2 points) a = -1 b = 8 c = 3 if b > c: if c > 0: print("yes!") elif b > 0: b = c-b elif a < 0: print("uhm") else: print("maybe") if b!= c: print (b) else: print("no.") else: print("finish!") Solution: Yes! 8 (e) (8 points) def funct(num): go = True while go == True: print("loop running") if num%3 == 0: go = False print("change go") num = num - 1 print("fun") return num print( funct(11) ) Solution: loop running fun loop running fun loop running change go fun 4

5 8 5

6 (f) (4 points) def abc(a, b): c = 3 if c < a: print("cs") if c > b: return a + b*c if c == 3: print("190") return b + a*c print( abc(10, 1) ) print( abc(2, 4) ) Solution: CS

7 3. (10 points) List manipulation. The statements below are executed in order in a python program. For each print statement, give the output. If the print statement would cause an error, you may just write error and continue to the next statement. list = ["Mary", "John", -10, 4, 4.2, True] x = 3 print(list[1]) print(list[x]) list[0] = "Juan" list[1] = "Maria" print(list) print(list[5] and not(list[2] <= x)) print(list[list[x]]) list = list + [12, False] print(list) print(list + 12) list2 = list[3:6] print(list2) print(len(list2) + len(list)) print(list[10]) 7

8 Solution: "John" 4 ["Juan", "Maria", -10, 4, 4.2, True] False 4.2 ["Juan", "Maria", -10, 4, 4.2, True, 12, False] error: can t "concatenate" list using + int [4, 4.2, True] 11 error: index out of bounds 8

9 4. Prof. Summet is writing a function identify prime numbers (numbers which are only divisible by 1 and themselves). For example: 4 is not a prime number (divisible by 2) while 5 is a prime number. The function should return True if the number is prime and False if the number is not prime. However, her code isn t working as expected! 1 def isprime(num) 2 p = True 3 i = 1 4 while i <= num: 5 if num % i == 0: 6 p = False 7 i = i return p (a) (2 points) As currently written, what will the function return for the function call isprime(4)? Solution: False (b) (2 points) As currently written, what will the function return for the function call isprime(5)? Solution: False (c) (4 points) Explain Prof. Summet s logical error(s) and correct it/them. You do not need to rewrite the entire program, only the problematic lines of code. Solution: The bounds (starting and stopping values) of the loop are incorrect. Since all numbers (not just primes) are divisible by 1, Python will always calculate that num % 1 == 0 is True and thus it will be identified as not a prime number (ie the function will return False). To correct it, we should change the initialization on line 3 to i = 2 Note we must also change the loop on line 4 to while i < num:. Otherwise, you will see the same result (returning False for all numbers) since all numbers are divisible by themselves. Technically, you would also need to identify 2 as a prime number, but this is a simple: if num == 2: return True at the beginning of the method, and I didn t grade for this identification. 9

10 5. (5 points) Write a function called countup that accepts two integer parameters. The function will print out all integers between the two parameters(excluding both parameters!) in ascending order using a while loop. You may assume that the two parameters are valid integers, and that the first parameter will always be smaller than the second parameter. Note that you may not use a for loop in your solution! For example, countup(1, 5) would print the numbers 2 3 and 4 to the screen (on separate lines) Solution: def countup(num1, num2): num1 = num1 + 1 while num1 < num2: print(num1) num1 = num1 + 1 Scoring: +2 for a correct function header. +2 for correct while loop (bounds) +1 for correct numbers being printed 10

11 6. (7 points) Write a function named bounds which takes two parameters: 1) an integer and 2) a boolean. The function should return a boolean value. It should return True if the integer is in the range , inclusive. If the boolean parameter is True, then the function should return True if the number is outside the range of (inclusive) (ie the integer is less than 1, or greater than 100). Examples: bounds(50, False) returns True bounds(101, False) returns False bounds(101, True) returns True Solution: def bounds(n, backwards): if backwards == True: return n < 1 or n > 100 else: return 1 <= n <= 100 Scoring: +2 function definition +2.5 handles numbers inclusive you can test your code with bounds(50, False) which should return True and bounds(50, True) which should return False handles numbers outside inclusive you can test your code with bounds(101, False) which should return False and bounds(101, True) which should return True. 11

12 7. (9 points) Write a function named maxlist which takes two lists as parameters. The function should return a new list which contains the maximum value at each index when the lists are compared value-by-value. You may assume the lists have at least 1 element and are of the same length. Examples: maxlist([1, 4, 10], [3, 2, 9]) returns [3, 4, 10] maxlist([9], [10]) returns [10] maxlist([-5, 10], [11, 10]) returns [11, 10] Solution: def maxlist(list1, list2): list3 = [] for i in range(len(list1)): if list1[i] > list2[i]: list3.append(list1[i]) else: list3.append(list2[i]) return list3 Scoring: +2 function definition +2 loops over lists +2 determines maximum element correct +2 makes new list & stores max value into it +1 returns new list 12