Introduction to Programming Department of Computer Science

Introduction to Programming Department of Computer Science and Information Systems Lecturer: Steve Maybank [email protected] Spring 2020 Revision of the Summer 2017 Examination Birkbeck College, U. London 1

Question 1a Which of the following are names of variables 3y6 3y 6 Y3-6 # adjacent underscores p08 Birkbeck College, U. London 2

Rules for the Names of Variables The only characters allowed are numbers, letters and underscore A name cannot begin with a number Birkbeck College, U. London 3

Question 1b What are the final values of a, b, c, d, e? p 3 q 2 a p q*4 b 10**p**q c 5*p-q/5 d 5-(4-(3-(2-p))) e p%2 q%2 Birkbeck College, U. London 4

Operators and Precedence Exponentiation: ** Times: * Real Division: / Plus: Minus: - Remainder: % Apply the highest precedence operator first: 25%2**3 If the operators have the same precedence then evaluate left to right: 25%3*8 Birkbeck College, U. London 5

Question 2b A swimming pool with volume poolVolume litres is initially empty. Water enters at inSpeed litres/min, but leaks away at outSpeed litres/min. Find the number mFill of minutes required to fill the pool. (inSpeed - outSpeed) *Mfill poolVolume Note the camel case names Birkbeck College, U. London 6

Volume of Water The volume entering the pool in one minute is (inSpeed-outSpeed)*1 The volume entering the pool in mFill minutes is (inSpeed-outSpeed)*mFill The definition of mFill ensures that the last quantity is the pool volume. Birkbeck College, U. London 7

Question 2c A train with an average speed of 100km per hour travels from L to B in 3 hours, but it has to wait at B. As a result, the average speed is reduced to 90km per hour. Find the waiting time. 90 distance/totalTime distance/(journeyTime waitingTime) 300/(3 waitingTime) waitingTime 1/3 hours Birkbeck College, U. London 8

Question 3 Find five errors in the code import 0 # import is a reserved word if export import : # export not defined import 3.0 export 3E-5 print("import is" 3.0) # string number else # missing colon export export//import # division by zero Birkbeck College, U. London 9

Question 4 Write code to show "Please enter the price:" in the shell and to return a value entered at the keyboard. The returned value is converted to floating point and assigned to a variable price. price float(input("Please enter the price:" )) Birkbeck College, U. London 10

Question 4, Second Part What is the value of price for each of these inputs in the shell Please enter the price: 5 # 5.0 Please enter the price: "5" # error Please enter the price: 6.2 #6.2 Please enter the price: 5*6.2 # error Birkbeck College, U. London 11

Question 4, Part c (i) What is printed when the following code is run? print("He said\n\"Hello\" and 'Goodbye'\ntoday.") "He today." said\n \"Hello\" 'Goodbye' \ntoday # The quotes contain a string # \n is new line # \" is a character in a string # ' is a character in a string # \n is new line Birkbeck College, U. London 12

Question 4, Part c (ii) and (iii) What is printed when the following code is run? houseNumber 32 streetName “Hamilton Road” print(houseNumber streetName) print(len("\\"*3 "Harry")) "\\" "\\"*3 # string with the single character backslash # repeat the string three times # string concatenation Birkbeck College, U. London 13

Question 4, Part c (iv) and (v) What is printed when the following code is run? firstName "Mickey" lastName "Mouse" print(firstName[3], lastName[-3]) names ["Amir", "Barry", "Chris", "Dylan"] print(names[-1][-1]) Birkbeck College, U. London 14

Question 5a What is printed? Use to indicate a space temperature 39.8954 print("A:", "%d" % temperature) A: 39 # %d implies integers print("B:", "%.f" % temperature) B: 40 # %.f implies floating point, no fraction Birkbeck College, U. London 15

Question 5a Continued 1 What is printed? Use to indicate a space temperature 39.8954 print("C:", "%s" % temperature) C: 39.8954 # %s implies string print("D:", "%06.2f" % temperature) D: 039.90 # %06.2f implies a field width # of 6, 2 decimal places and 0 padding Birkbeck College, U. London 16

Question 5a Continued 2 What is printed? Use to indicate a space temperature 39.8954 print("E:", "%-7d%%" % temperature) E: 39 % # %-7d implies integer # in a field of width 7 and left justified. # %% implies a single character % Birkbeck College, U. London 17

Question 5b Write code to print the following using a multiple format specifier Temperature: 39.9 C Feeling: Great st1 "Temperature: %4.1f C Feeling: %7s" # %4.1f implies a field of width 4 and 1 decimal place # %7s implies a string in a field of width 7 print(st1 % (temperature, "Great")) Birkbeck College, U. London 18

Question 6a Explain how the lexicographic ordering for characters is extended to give a lexicographic ordering for strings Let a, c1, c2 be any strings. Let b1, b2 be distinct characters, i.e. strings of length 1. st1 a b1 c1 st2 a b2 c2 If b1 b2 then st1 st2. If b1 b2 then st1 st2 Birkbeck College, U. London 19

Question 6b space numbers uppercase lowercase True or False: "1" "2" "cart" "carp" "milestone" "mile stone" "Corn" "2Corn" "car" "care" Birkbeck College, U. London 20

Question 7a wind speed description s 1 calm 1 s 3 light air 3 s 7 light breeze 7 s out of range Write nested if statements to print the correct descriptions given a non-negative value of s. Use if elif else. Birkbeck College, U. London 21

Question 7a Continued wind speed description s 1 calm 1 s 3 light air 3 s 7 light breeze 7 s out of range if s 1: print("calm") elif s 3: print("light air") elif s 7: print("light breeze") else: print("out of range") Birkbeck College, U. London 22

Question 8a What is printed when the following code is run? sumSquares 0 for x in range(3): sumSquares sumSquares x*x print(sumSquares) # x in range(3), so x takes the values 0, 1, 2 Birkbeck College, U. London 23

Question 8b What is printed when the following code is run? sumSquares 0 for x in range(3): sumSquares sumSquares x*x print(sumSquares) # x in range(3), so x takes the values 0, 1, 2 Birkbeck College, U. London 24

Question 8c large float(input("Enter a number:")) position 1 Write code to input 6 numbers for i in range(2, 7): and then print out x float(input("Enter a number:")) the position of if x large: the largest number. large x position i print("position of largest no:", position) Birkbeck College, U. London 25

Question 9a Identify in the following code the name of a variable, the name of a function and the values of the arguments to a function quantity 5*8 price round(6.8275, 2) Birkbeck College, U. London 26

Question 9c describe the compile time error in the code. def main(): result cubeVolume(2) print("side length 2, volume", result) main() def cubeVolume(sideLength): if (sideLength 0) : return 0 return sideLength**3 Birkbeck College, U. London 27

Question 9d Identify the branches in the function cubeVolume def cubeVolume(sideLength): if (sideLength 0) : return 0 volume sideLength**3 return volume Birkbeck College, U. London 28

Question 10b What is the length of the list scores? Which non-negative integers can be indices to scores? scores [17, 5, 3] Birkbeck College, U. London 29

Question 10c Which number is printed by the following code? scores [17, 5, 3] values scores scores[0] 10 print(values[0])# two names but only one list of numbers Birkbeck College, U. London 30