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

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
```
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.

Consider the following program:

 1  def mystery(word, letter):
 2      print("word: %s" % (word))
 3      print("letter: %s" % (letter))
 4      result = ""
 5      for ch in word:
 6          if ch != letter:
 7              result += ch
 8
 9      # draw stack here
10      return result
11
12  def main():
13      test = "hello"
14      check = "l"
15      answer = mystery(test, check)
16      print("the answer is %s" % (answer))
17
18  main()

Draw the function stack as it would appear when you reach line 9. (In gradescope you will need to upload your picture. Be sure you can do this by taking the practice quiz in gradescope.) [answer]
What variables are in scope at line 9?
What is the program’s output (i.e. what does it print when the program is run)?
What does the mystery function do?
What would mystery("moobaalalala", "a") return?
What would mystery("zoo", "a") return?

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

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?

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()

Draw the function stack as it would look the first time is_odd() is called. [answer]
What variables are in scope at this point in the code?
What is the program’s output (i.e. what does it print when the program is run)?
What does the enigma() function do?

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!
```