Lab_05-CS171

CS 171 - Lab 5 Professor Mark W. Boady and Professor Adelaida Medlock Content by Professor Mark Boady Detailed instructions to the lab assignment are found in the following pages. • Complete all the exercises and type your answers in the space provided. What to submit: • Lab sheet in PDF • A screenshot of code and execution for questions 23, 24, 25 Submission must be done via Gradescope • Please make sure you have tagged all questions when you upload • We only accept submissions via Gradescope. Student Name: Aryan Dixit User ID (abc123): 14479032 Possible Points: 88 Your score out of 88 : Lab Grade on 100% scale: Graded By (TA Signature):

CS 171 Lab 5 Week 5 1. Critical Thinking Questions Question 1: 7 points Closely examine the Python program below. FYI: A looping structure allows a block of code to be repeated one or more times. A while loop is one of the two looping structures available in Python. (a) (2 points) In the Python code, circle / highlight all the lines executed during each iteration of the loop. • name = input("Enter your name:") • x = 0 • while (x < 20): • print(name) • x = x + 1 • print("The End") (b) (1 point) In the IDE, enter and test the code. What does the line of code: x = x + 1 do? The line of code x = x + 1 increments the value of the variable x by 1 in each iteration of the loop. (c) (1 point) How does the Python interpreter know what lines of code belong to the loop body? The Python interpreter knows what lines of code belong to the loop body based on their level of indentation. All the lines indented under the while statement with while (x < 20): are considered part of the loop body. (d) Every loop structure requires three actions. Identify the line of code in the Python program that corresponds to each of the three actions. (a) (1 point) Initialize a variable used in the test condition: Line of code: x = 0 (b) (1 point) Include a test condition that causes the loop to end when the condition is false: # Description: This program prints # a person’s name 20 times name = input ("Enter your name: ") x = 0 while (x < 20): print (name) x = x + 1 print ("The End")

CS 171 Lab 5 Week 5 print(number) number = number + 1 Question 4: 3 points Enter and execute the following code: number = 1 while number < = 10: print (number) number − = 1 (a) (1 point) Does the program end? No, the program will not end because there is no logic to stop the loop. It will result in an infinite loop. (b) (2 points) How could you fix this problem? number = 1 while number <= 10: print(number) number += 1 Question 5: 4 points Enter and execute the following code: number = 1 while number < = 10: if number % 2 == 0: print (number, end= " ") number = number + 1 (a) (1 point) State the output 2 4 6 8 10 (b) (1 point) What caused the output to display on one line? The output is displayed on one line because of the end=" " argument in the print statement. This argument specifies the character to be printed at the end of the printed text. In this case, it's a space character, so the numbers are separated by spaces on the same line. (c) (2 points) What control structures are used in this code? The control structures used in this code are: • while loop: It controls the repetition of the code block as long as the condition number <= 10 is true. • if statement: It is used to check whether number is even ( number % 2 == 0 ) and only then prints the number. Question 6: 7 points

CS 171 Lab 5 Week 5 The following directions will create a program that prompts the user to enter a number between 1 and 10. As long as the number is out of range the program re-prompts the user for a valid number. Complete the following steps to write this code. (a) (1 point) Write a line of code that prompts the user for a number between 1 and 10. number = int(input("Enter a number between 1 and 10: ")) (b) (1 point) Write a Boolean expression that tests the number the user entered by the code in step (a) to determine if it is not in range. out_of_range = (number < 1) or (number > 10) (c) (2 points) Use the Boolean expression created in step (b) to write a while loop that executes when the user input is out of range. The body of the loop should tell the user that they entered an invalid number and prompt them for a valid number again. while out_of_range: print("Invalid number. Please enter a number between 1 and 10.") number = int(input("Enter a number between 1 and 10: ")) out_of_range = (number < 1) or (number > 10)

CS 171 Lab 5 Week 5 (c) (1 point) Within the loop body, update the variable used in the test condition: Write the code for the loop body. number = int(input("Enter a positive number (enter a negative number or zero to exit): ")) (d) (1 point) Is this a count-controlled loop? This is not a count-controlled loop. It is condition-controlled because the loop continues until a certain condition (input being greater than zero) is met. (e) (1 point) Complete the program. Enter your fully functioning code below. total = 0 number = int(input("Enter a positive number (enter a negative number or zero to exit): ")) while number > 0: total += number number = int(input("Enter a positive number (enter a negative number or zero to exit): ")) print("The total is:", total) FYI: Short-cut operators provide a concise way of creating assignment statements when the variable on the left-hand side of the assignment statement is also on the right-hand side. The addition short-cut operator ( += ) is usually used for incrementing a variable. These are also called compound operators. Question 8: 5 points Enter and execute the following code: number = 1 number += 3 print (number) (a) (1 point) What does the += shortcut operator do? The += shortcut operator adds the value on the right-hand side to the variable on the left-hand side and assigns the result back to the variable. In this specific code, number += 3 adds 3 to the variable number , so it's equivalent to number = number + 3 . The value of number becomes 4. (b) (1 point) The code: x += 5 is equivalent to which of the following lines of code? x = 5 x = y + 5 x = x + 5 y = x + 5 The code x += 5 is equivalent to the line of code: x = x + 5 . It adds 5 to the variable x . (c) Replace the operator += with the following shortcut operators and execute the code. Explain what each operator does.

CS 171 Lab 5 Week 5 (a) (1 point) -= The -= operator subtracts the value on the right-hand side from the variable on the left-hand side and assigns the result back to the variable. For example, x -= 2 is equivalent to x = x - 2. (b) (1 point) *= The *= operator multiplies the variable on the left-hand side by the value on the right-hand side and assigns the result back to the variable. For example, y *= 4 is equivalent to y = y * 4. (d) (1 point) Is the following line of code valid: 23 += total ? Why or why not? The line of code 23 += total is not valid. The += operator can only be used with variables, not with constant values like 23 . You can use += to update the value of a variable by adding to it, but it can't be used to modify a constant value. Question 9: 2 points Enter and execute the following code: bonus = 25 salary += bonus print ("Total salary:", salary ) (a) (1 point) What is the output of the preceding code? The code as given will produce an error because it tries to add the value of bonus to a variable salary without first initializing salary . The code is attempting to perform an operation on an undefined variable. (b) (1 point) Rewrite the code so that it produces valid output. salary = 1000 # Initialize salary to some value bonus = 25 salary += bonus print("Total salary:", salary) Question 10: 1 point The following code should print the numbers beginning with 100 and ending with 0. However, it is missing a line of code. Add the missing code, using the shortcut operator. Draw an arrow to indicate where the code belongs. countdown = 100 while countdown > = 0: print (countdown) print ("Done!") countdown = 100 while countdown >= 0:

CS 171 Lab 5 Week 5 What happens if you replace the + with a , ? print("First letter of " + word + " is " + word[0]) Question 12: 3 points Examine the code below. name = "Simone" cost = 3.56 numApples = 89 What type of data is stored in each variable? (integer, floating point, or string) (a) (1 point) name : name stores a string. (b) (1 point) cost : floating point (c) (1 point) numApples : stores an integer. FYI: A variable that can store only the values True and False is called a Boolean variable. Question 13: 1 point Given the assignment statement: foundCost = False What type of data is stored in foundCost ? `foundCost` stores a Boolean data type, specifically the value `False`, which is a boolean literal in Python. Question 14: 3 points Enter and execute the following two Python programs. WHILE LOOP name = input ("Enter your name: ") x = 0 while x < 20: print (name) x = x + 1 FOR LOOP name = input ("Enter your name: ") for x in range (20): print (name) (a) (2 points) What is the output for each program? The output for both programs will be the same. They both print the name entered by the user 20 times. For example, if the user enters "John," the output will be "John" repeated 20 times. (b) (1 point) Both programs produce the same output. Which code fragment is more concise?

CS 171 Lab 5 Week 5 The "FOR LOOP" code is more concise. It accomplishes the same task as the "WHILE LOOP" code with fewer lines of code and is generally considered more Pythonic and easier to read. FYI: The Python predefined function range() is used to define a series of numbers and can be used in a FOR loop to determine the number of times the loop is executed. Question 15: 5 points Enter and execute the following code fragments and state the output: (a) (1 point) for x in range (5): print (x , end=" ") 0 1 2 3 4 (b) (1 point) for x in range (1 ,5): print (x , end=" ") 1 2 3 4 (c) (1 point) for x in range (3 ,20 ,2): print (x , end=" ") 3 5 7 9 11 13 15 17 19 (d) (1 point) numIterations = 6 for x in range ( numIterations ): print (x , end=" ") 0 1 2 3 4 5 (e) (1 point) numIterations = 6 for x in range (1 , numIterations +1): print (x , end=" ") 1 2 3 4 5 6 Question 16: 3 points After examining the five code fragments in question 15, explain how the range() function works. Include an explanation of the arguments.

CS 171 Lab 5 Week 5 favorite = input ("Enter your favorite ice cream flavor: ") for x in range (1 ,5): print ( str (x) + "." , favorite , end="\t") (a) (1 point) What does the program do? The program prompts the user to enter their favorite ice cream flavor, and then it uses a for loop to print the user's favorite ice cream flavor followed by the numbers from 1 to 4, all on the same line and separated by tabs. (b) (1 point) Why is the str() function needed in the print statement? The str() function is used to convert the number x to a string so that it can be concatenated with the favorite ice cream flavor in the print statement. Without str() , you can't concatenate a number directly with a string, so it's necessary to convert x to a string to include it in the output. Question 19: 3 points Complete the arguments in the following range() function so that the code prints the even numbers between 100 and 200, inclusive. for x in range ( ??? ) print (x) Question 20: 3 points Complete the arguments in the following range() function so that it prints: 5 4 3 2 1 0 . for x in range ( ??? ) print (x) for x in range(5, -1, -1): print(x) FYI: An accumulator is a variable that stores the sum of a group of values. Question 21: 5 points Examine the following code segment. 1 2 3 4 5 total = 0 for x in range (5): number = int ( input ("Enter a number: ")) total += number print ("The total is:" , total ) (a) (1 point) Why is the variable total initialized to 0 in the first line of code? The variable total is initialized to 0 in the first line of code because it is used to accumulate the sum of the numbers entered by the user. By initializing it to 0, we start with a clean slate, and we can add the user's input to it in the subsequent loop.

CS 171 Lab 5 Week 5 (b) (1 point) Explain what line 3 of the code does. Line 3 of the code prompts the user to enter a number using the input() function and then converts the user's input to an integer using int() . It stores the entered number in the variable number . (c) (1 point) Explain what line 4 of the code does. Line 4 of the code adds the value of the number (the user's input) to the total variable. It accumulates the sum of the numbers entered by the user in each iteration of the loop. (d) (1 point) How many numbers does the program prompt for? The program prompts for numbers in the loop with for x in range(5): , which means it prompts for numbers five times. (e) (1 point) What is the accumulator in the code segment? The accumulator in the code segment is the variable total . It accumulates the sum of the numbers entered by the user, and its value keeps increasing with each input. Question 22: 1 point Is it better to use a for loop when you know the number of times the loop should be executed or when you do not know? It's better to use a for loop when you know the number of times the loop should be executed. For situations where you have a fixed, predetermined number of iterations, a for loop provides a more concise and straightforward way to manage the looping process. Use the Python Interpreter for these questions. Submit one or more screenshots for each. Show your full source code and an example of the code executing. Question 23: 3 points Write a code segment using a FOR loop that prints multiples of 5 from 5 to 500, one on a line.

CS 171 Lab 5 Week 5