Quiz 3 Study Guide

You are responsible for all material needed for Labs 1-5 which includes for loops, if statements, boolean operators, relational operators, while loops, and functions.

Study guides are not graded. You may work with other students on the questions, and ask questions about the guide during evening ninja help sessions, on Slack, or with meetings with faculty and staff. We do not provide full solutions to the study guides.

In addition to all concepts from Quiz 2, you should understand the following:

Python concepts

  • while loops with flag variables

  • stack diagrams

  • scope of a variable

  • function definition

  • function call

  • function parameters

  • function arguments

  • functions with returns

  • functions done for side effects

  • mutable and immutable types

  • list manipulation (accumulators, indexing, etc)

Practice problems

  1. Write a program which asks the user for 4 words and then prints them in reverse order. Hint: store them in a list.

    Here’s an example run of the program:

    word 1: hello
    word 2: zebra
    word 3: unicorn
    word 4: corgi
    corgi
    unicorn
    zebra
    hello
  2. Write a function called avgList that, given a list of numbers, calculates and returns their average. For example, avgList([5, 10, 5, 4]) should return 6. Write a main function to test the function in a complete program.

  3. Consider the following program:

    def mystery(word, letter):
        print("word: %s" % (word))
        print("letter: %s" % (letter))
        result = ""
        for ch in word:
            if ch != letter:
                result += ch
    
        # draw stack here
        return result
    
    def main():
        test = "hello"
        check = "l"
        answer = mystery(test, check)
        print("the answer is %s" % (answer))
    
    main()
    1. Draw the function stack as it would look just prior to returning from helper. [answer]

    2. Which variables are in scope at this same point in the code?

    3. What is the program’s output (i.e. what does it print when the program is run)?

    4. What does the mystery function do?

    5. What would mystery("moobaalalala", "a") return?

    6. What would mystery("zoo", "a") return?

  4. Write a program that reads in student grades from the user, until the user enters a -1. After reading in the -1, the program should compute and display the average grade.

    Please enter your grades below.  Enter a -1 when you are all done
    
    grade  1: 98
    grade  2: 87
    grade  3: 65
    grade  4: 95
    grade  5: 80
    grade  6: -1
    
    The average of those 5 grades is 85.000
  5. Analyze the following code:

    m = ["t","i","m","e"]
    s = "time"
    m[1] = "a"
    s[1] = "a"

    What happens when this code is executed? What are the values of m and s afterward?

  6. Consider the following program:

    def is_odd(number):
       # Q1: draw stack here (the first
       #     time the function is called)
       if number % 2 == 0:
          return False
       else:
          return True
    
    def enigma(ls):
       total = 0
       for i in range(len(ls)):
          if is_odd(ls[i]):
             ls[i] = ls[i]*2
          total = total + ls[i]
       return total
    
    def main():
       values = [5,3,4,8]
       print(values)
       result = enigma(values)
       print("result: %d" % result)
       print(values)
    
    main()
    1. Draw the function stack as it would look the first time is_odd() is called. [answer]

    2. What variables are in scope at this point in the code?

    3. What is the program’s output (i.e. what does it print when the program is run)?

    4. What does the enigma() function do?

  7. Write a function called getInt that has two parameters, lo and hi. The function should prompt the user to enter an integer between lo and hi (inclusive), and then return the value entered. Your function should not return until the user enters a valid integer in the range lo to hi. You may assume both lo and hi are positive integers.

    Now add a main() function that calls getInt to get an integer from 1-10. Your main() should then print out "Boo!" that many times.

    Here’s an example run of the full program:

    Please enter an integer from 1-10: 99
    Please enter an integer from 1-10: -40
    Please enter an integer from 1-10: 4
    Boo!
    Boo!
    Boo!
    Boo!