Problem Set 5

Part I due by 11:59 p.m. on Thursday, October 24, 2023.
Part II due by 11:59 p.m. on Sunday, October 27, 2023.

Preliminaries

In your work on this assignment, make sure to abide by the collaboration policies of the course.

If you have questions while working on this assignment, please come to office hours, post them on Piazza, or email cs111-staff@cs.bu.edu.

Make sure to submit your work on Gradescope, following the procedures found at the end of Part I and Part II.

Part I

Problem 0: Reading and response

5 points; individual-only

Grace Murray Hopper was one of the pioneers of computer science. Among other things, Hopper played an important role in the transition from low-level programming (using binary machine-language instructions that the CPU could execute directly) to programming in higher-level languages like Python.

This week’s reading involves a biographical sketch of Hopper that provides an overview of her impressive career.

After reading this piece, create the necessary file for your response by taking the following steps:

1. Access the template that we have created by clicking on this link and signing into your Google account as needed.

2. When asked, click on the Make a copy button, which will save a copy of the template file to your Google Drive.

3. Select File->Rename, and change the name of the file to ps5pr0.

In your copy of ps5pr0, write a response that addresses the following question:

According to the piece, Grace Murray Hopper was instrumental in “opening up new worlds to computing.” How did she do this? What do you find most impressive about her work?

Once you have completed your response, choose File→Download→Plain Text, and save the file on your machine. The resulting file (ps5pr0.txt) is the one that you will submit. See the submission guidelines at the end of Part I.

Installing and using Logicly

In the rest of this assignment you will design several digital circuits using a circuit-design tool called Logicly. If you haven’t already installed Logicly on your own computer, you should do so now:

Installing and Using Logicly

(Important: Although it’s possible to use Logicly in your browser, you need to download it in order to be able to save your work.)

That page also includes guidelines for how to use Logicly – including a link to a video that provides a good overview of the program.

Important: There appears to be a bug in Logicly that causes it to occasionally display red wires. If this happens, save your file, close down Logicly, and then reopen it. This will typically fix the problem.

Working on the virtual desktop

If you can’t get Logicly to work on your own computer, you can use it on the virtual desktop. Instructions for using the virtual desktop can be found here.

Obtaining the circuit starter files

Download the following zip file: ps5_circuits.zip

Unzip this archive, and you should find a folder named ps5_circuits, and within it a starter file for each of the circuit problems.

Problem 1: XOR

5 points; individual-only

Open the ps5pr1.logicly starter file in Logicly (see above for how to obtain the starter files).

The XOR function takes two inputs (x and y), and it outputs a 1 if and only if exactly one of its inputs is 1. It has the following truth table:

  inputs  |
  x    y  | output
-------------------
  0    0  |   0
  0    1  |   1
  1    0  |   1
  1    1  |   0

Build a circuit for the XOR function using the minterm expansion principle that we discussed in lecture. The resulting circuit should use only AND, OR, and NOT gates.

Notes:

• We’ve provided you with switches for the inputs x and y, as well as with a NOT gate for the negation of each input. For example, the leftmost switch is for x itself, and the NOT gate immediately to its right is for NOT x. We have also provided you with a light bulb for the output. You must use these components in your circuit, and you should not change their properties.

• You are welcome to move the provided components as needed, but please keep their relative positions the same. For example, the inputs should remain at the top of your circuit, and x should be to the left of y.

• Use the Selection Tool to drag the necessary logic gates into your circuit and to add the necessary wires. See the overview video for more detail.

• You may also find it helpful to use the Pan Tool (the icon at the top of the screen that looks like a hand – or possibly a different icon that looks like crossed green arrows) and the magnification slider available in the lower right-hand corner to adjust how much of your circuit is visible. After using the Pan Tool, don’t forget to switch back to the Selection Tool.

• Test your circuit by clicking the input switches to turn them on and off. Check to see if you obtain the correct output for all possible inputs. Remember that XOR should output a 1 if and only if exactly one of the two inputs is a 1.

• Once this circuit is working, save your work by using the File->Save menu option.

Problem 2: Full Adder

25 points; pair-optional

This is one of only two problems that you may complete with a partner. See the rules for working with a partner on pair-optional problems for details about how this type of collaboration must be structured.

Open the ps5pr2.logicly starter file in Logicly. If you are working with a partner, there is a text block at the top of this subcircuit for your partner’s name and email (if any). To add the necessary information, select the text block with the Selection Tool (the arrow) and edit the Text in the Label Properties pop-up window.

Build a Full Adder (FA) as described in lecture, using the minterm expansion principle to create a circuit that uses only AND, OR, and NOT gates.

Remember that a Full Adder adds a single column of digits from the bitwise sum of two binary numbers. It takes three inputs:

• x and y, the two bits being added from this column of the addition
• c_in, the carry bit into this column of the addition

and it should produce two separate outputs:

• s, the bit from the sum that would go at the bottom of this column of the addition
• c_out, the carry bit out of this column of the addition.

See below for how to export your Full Adder so that it can be used in later problems.

Notes:

• After opening the file, you may need to use the Pan Tool (the hand icon available at the top of the screen) and the magnification slider available in the lower right-hand corner to see all of the provided components. After using the Pan Tool, don’t forget to switch back to the Selection Tool.

• We’ve provided you with the three inputs and the two outputs, as well as with NOT gates for the inputs. You must use the provided inputs and outputs, and you should not change their properties.

• You can adjust the positions of the inputs and output as needed, but please keep their relative positions the same.

• You should start with the truth table for a Full Adder. You can write it out yourself, or you can use the one that we gave you in the lecture notes. Once you have the truth table, you should apply the minterm expansion principle twice: once to obtain a circuit that will produce the correct outputs for s, and once to obtain a circuit that will produce the correct outputs for c_out.

• Don’t try to simplify your circuit, and don’t use gates other than AND, OR, and NOT. The purpose of this problem is to practice using the minterm expansion principle. (Note: Logicly provides a sample Full Adder circuit, but it uses an approach other than minterm expansion, so it’s not useful for this problem.)

• Here again, you should test your circuit by clicking the input switches to turn them on and off. Once this circuit is working, save your work by using the File->Save menu option.

• Exporting your Full Adder: Because you will use your Full Adder in later problems, you should take the following steps to export it:

  1. Use the Edit->Select All menu option to select the entire circuit.

  2. Click the building block icon (which looks like a Lego piece) at the top of the screen. (Alternatively, you can select the Edit->Create Integrated Circuit menu option.)

  3. In the window that pops up, give your circuit a name (e.g., Full Adder) by entering it in the Full Name text box. You can also add a Symbol Label, but doing so is not required.

  4. Click the Create IC button to create the integrated circuit.

  5. Use the File->Export Integrated Circuit Library menu option to export your work. Give the file an appropriate name (e.g., full_adder) and save it in a place where you can easily find it.

Problem 3: 4-Bit Ripple-Carry Adder

15 points; individual-only

Open the ps5pr3.logicly starter file in Logicly.

Build a 4-Bit Ripple-Carry Adder. We examined a 2-Bit Ripple-Carry Adder in lecture; this problem requires you to extend that circuit to a 4-bit version.

Recall that a Ripple-Carry Adder combines multiple Full Adders to produce a circuit that adds two binary numbers. Each Full Adder handles one column of the addition. The circuit as a whole takes eight inputs:

• the 4 bits of one of the numbers: x3, x2, x1, and x0
• the 4 bits of the other number: y3, y2, y1, and y0

and it should produce five outputs (s4, s3, s2, s1, and s0) that correspond to the five bits of the sum. The relationships between the inputs and the outputs are shown below:

   x3 x2 x1 x0
+  y3 y2 y1 y0
--------------
s4 s3 s2 s1 s0

Note that the sum has five bits to accommodate the possibility of a carry.

This circuit should not be built using the minterm expansion principle. Rather, it should be built by combining four instances of your Full Adder circuit.

See below for information about how to import your Full Adder, as well as for the steps needed to export Ripple-Carry Adder so that it can be used in later problems.

Notes:

• Here again, you should use the Pan Tool and the magnification slider as needed to see all of the provided components.

• You must use the provided inputs and outputs. Please keep their relative positions the same, and do not change their properties. (Note that we haven’t provided NOT gates for the inputs because you won’t need to negate them.)

• Using Your Full Adder:

  1. Use the File->Import Integrated Circuit Library menu option to import the file in which you stored your exported Full Adder circuit. (If you haven’t already exported your Full Adder, do so now by following the steps from the last note of the previous problem.)
  2. After importing the file, scroll down to the bottom of the left-hand pane of components. You should see a section labeled Custom that contains a building block for your Full Adder.
  3. You can insert a copy of your Full Adder into your circuit by using the Selection Tool to drag the Full Adder building block into the circuit. You should see a box that looks like this:
     
     
     
     
  4. It will be easier to use a Full Adder if you rotate it clockwise. To do so, select a Full Adder box and click the Rotate Clockwise icon at the top of the screen (or choose the Edit->Rotate Clockwise menu option). After rotating, the Full Adder box should look like this:
     
     
     
     

• You will need a c_in of 0 on the far right of the Ripple-Carry Adder. Use the built-in component labeled Low Constant for this purpose. Simply drag it into your circuit and connect it to the appropriate input of the rightmost FA.

• Here again, you should test your circuit by clicking the input switches to turn them on and off. Once this circuit is working, save your work by using the File->Save menu option.

• Exporting your Work: Because you will use your 4-Bit Ripple Carry Adder in later problems, you should take the following steps to export it:

  1. Use the Edit->Select All menu option to select the entire circuit.

  2. Click the building block icon (which looks like a Lego piece) at the top of the screen. (Alternatively, you can select the Edit->Create Integrated Circuit menu option.)

  3. In the window that pops up, give your circuit a name (e.g., 4-Bit Ripple-Carry Adder) by entering it in the Full Name text box. You can also add a Symbol Label, but doing so is not required.

  4. Click the Create IC button to create the integrated circuit.

  5. Use the File->Export Integrated Circuit Library menu option to export your work. Note that you will end up exporting both your Full Adder (since you imported it for this problem) and your Ripple-Carry Adder. Give the file an appropriate name (e.g., both_adders) and save it in a place where you can easily find it.

Problem 4: 4x1 Multiplier

10 points; individual-only

Open the ps5pr4.logicly starter file in Logicly.

Build a 4x1 multiplier in the space provided. This circuit takes five inputs:

• the 4 bits of the first factor: x3, x2, x1, and x0
• the 1 bit of the other factor, y.

It will have four outputs (p3, p2, p1, and p0) that correspond to the four bits of the product. The relationships between the inputs and the outputs are shown below:

   x3 x2 x1 x0
*            y
--------------
   p3 p2 p1 p0

Because you are multiplying the first factor by either 0 or 1, the product can be computed very simply, using exactly four gates! Considering some concrete cases should help you to determine which gates you should use, and how they should be arranged. You should not need to employ the minterm expansion principle.

Notes:

• Here again, you should use the Pan Tool and the magnification slider as needed to see all of the provided components.

• You must use the provided inputs and outputs, and you must not change their properties. Please keep their relative positions the same.

• We’ve positioned the outputs at the bottom of the circuit, because doing so will make your circuit easier to use in the context of the next problem. Because of this, you may want to adjust the directions in which your gates are facing. After adding a gate to the circuit, you can rotate it by selecting it and then using one of the rotate icons at the top of the screen.

• As always, you should test your circuit by clicking the input switches to turn them on and off. Once this circuit is working, save your work by using the File->Save menu option.

• Exporting your 4x1 Multiplier: Because you will use your 4x1 Multiplier in the next problem, you should take the following steps to export it:

  1. Use the Edit->Select All menu option to select the entire circuit.

  2. Click the building block icon (which looks like a Lego piece) at the top of the screen. (Alternatively, you can select the Edit->Create Integrated Circuit menu option.)

  3. In the window that pops up, give your circuit a name (e.g., 4x1 Multiplier) by entering it in the Full Name text box. You can also add a Symbol Label, but doing so is not required.

  4. Click the Create IC button to create the integrated circuit.

  5. Use the File->Export Integrated Circuit Library menu option to export your work. Give the file an appropriate name (e.g., 4x1_multiplier) and save it in a place where you can easily find it.

Problem 5: 4x2 Multiplier

15 points; individual-only

Open the ps5pr5.logicly starter file in Logicly.

Build a 4x2 multiplier, which takes six inputs:

• the 4 bits of the first factor: x3, x2, x1, and x0
• the 2 bits of the second factor: y1 and y0.

and produces as outputs the six bits of the product: p5, p4, p3, p2, p1, and p0.

Your circuit should perform the computation shown below:

      x3 x2 x1 x0
   *        y1 y0
-----------------
p5 p4 p3 p2 p1 p0

You circuit should employ the “elementary-school” binary multiplication algorithm that we discussed in lecture. More specifically, you need to compute two partial products: the product of the top number (x3 x2 x1 x0) with the bit y0, and the product of the top number with the bit y1. You then need to add these partial products together in the appropriate way.

This circuit should not be built using the minterm expansion principle. Rather, it should be built by combining one or more instances of your 4x1 Multiplier and your 4-Bit Ripple-Carry Adder. See below for information about adding those components to your circuit.

Notes:

• Here again, you should use the Pan Tool and the magnification slider as needed to see all of the provided components.

• You must use the provided inputs and outputs, and you must not change their properties. Please keep their relative positions the same.

• You can insert one or more copies of your 4x1 Multiplier and 4-Bit Ripple-Carry Adder using the same procedure that you used to add instances of your Full Adder in Problem 3. In this case, you will need to import two files: the one containing both adders (i.e., your work from Problem 3), and the one containing your 4x1 Multiplier (i.e., your work from Problem 4).

• We recommend that you rotate each 4x1 Multiplier and 4-Bit Ripple-Carry Adder clockwise, following the procedure used to rotate your Full Adder in Problem 3. Doing so will cause each component’s inputs to be at the top of its box, and its outputs to be at the bottom of its box.

• You will need at least one constant in your circuit. See the notes that accompany Problem 3 for a reminder of how to add a constant.

• Don’t forget to test your circuit and save your work! During testing, you may find it helpful to use a calculator that can multiply in binary. Here are three options:

  • In Windows 10 or later, open the Calculator by searching for it from the Start menu. Then use the Programmer menu option, and choose the BIN option near the left-hand side of the window.

  • In older versions of Windows, open the Calculator by going to Start Menu->Accessories->Calculator. Then use the View->Programmer menu option, and choose the Bin option on the left-hand side of the window.

  • In Mac OS X, open the Calculator from /Applications, Spotlight, or Launchpad. Then select the View->Programmer menu option.

  • Write a function in Python that makes use of the base-conversion functions that you wrote for Problem Set 4!

Submitting your work for Part I

Login to Gradescope by clicking the link in the left-hand navigation bar, and click on the box for CS 111.

Important: You should submit a plain-text file for Problem 0, not a PDF. See Step 1 below as needed.

You should only submit the following files:

• ps5pr0.txt
• ps5pr1.logicly
• ps5pr2.logicly
• ps5pr3.logicly
• ps5pr4.logicly
• ps5pr5.logicly

You do NOT need to submit the files that Logicly produces when you export your components.

Here are the steps:

1. If you still need to create a plain-text file for Problem 0, open your ps5pr0 file on Google Drive, choose File->Download->Plain Text, and save the file on your machine.

2. Click on the name of the assignment in the list of assignments. You should see a pop-up window with a box labeled DRAG & DROP. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

3. Add your files to the box labeled DRAG & DROP. You can either drag and drop the files from their folder into the box, or you can click on the box itself and browse for the files.

4. Click the Upload button.

5. You should see a box saying that your submission was successful. Click the (x) button to close that box.

6. The Autograder will perform some tests on your files. Once it is done, check the results to ensure that the tests were passed. If one or more of the tests did not pass, the name of that test will be in red, and there should be a message describing the failure. Based on those messages, make any necessary changes. Feel free to ask a staff member for help.

   Note: You will not see a complete Autograder score when you submit. That is because additional tests for at least some of the problems will be run later, after the final deadline for the submission has passed. For such problems, it is important to realize that passing all of the initial tests does not necessarily mean that you will ultimately get full credit on the problem. You should always run your own tests to convince yourself that the logic of your solutions is correct.

7. If needed, use the Resubmit button at the bottom of the page to resubmit your work. Important: Every time that you make a submission, you should submit all of the files for that Gradescope assignment, even if some of them have not changed since your last submission.

8. Because your Logicly files have a format that Gradescope can’t read, you won’t be able to view those files on the Code page. Instead, you should click on the Download button for each Logicly file to download it. Once you have done so, open the downloaded file in Logicly to ensure that the uploaded file is the correct one.

Part II

Creating the necessary file

Problems 6, 7 and 8 will be completed in a single PDF file. To create it, you should do the following:

1. Access the template that we have created by clicking on this link and signing into your Google account as needed.

2. When asked, click on the Make a copy button, which will save a copy of the template file to your Google Drive.

3. Select File->Rename, and change the name of the file to ps5pr678.

4. Add your work for Problems 6, 7 and 8 to this file.

5. Once you have completed these problems, choose File->Download->PDF document, and save the PDF file on your machine. The resulting PDF file (ps5pr678.pdf) is the one that you will submit. See the submission guidelines at the end of Part II.

Problem 6: Practicing function calls, conditional execution and variable scope

10 points; individual-only

Consider the following Python program:

def foo(a, b):
    a += 4
    b *= 2
    c = mystery(a)
    print('foo', a, b, c)
    c += mystery(b)
    print('foo', a, b, c)
    return c

def mystery(c):
    a = c + 3
    if c > 8:
        a //= 2
        if a > 6:
            c -= 2
    elif c < 20:
        a += 1
        if a == 5:
            c += 1
    else:
        c -= 3
    return a

a = 2
b = 3
c = 8

print(a, b, c)
a = foo(b, c)
print(a, b, c)

In the Problem 6 section of ps5pr678, we have provided tables for you to complete. We have started some of the tables for you. You should:

• complete the variable tables so that they illustrate how the values of the variables change over time
• complete the output table so that it shows the output of the program (i.e., the values that are printed).

You may not need all of the rows provided in the tables.

Problem 7: Reviewing the range function

6 points; individual-only

As we saw earlier in the semester, range() is a built-in function that can be used to generate a sequence of integers. This function is often used in conjunction with for loops in Python, so it’s important that you fully understand how it works. Put your answers to the following questions in the Problem 7 section of ps5pr678.

1. What results do you obtain when you evaluate each of the following expressions in the console? (Note: In order to see the sequence that the range function generates, you need to use the list function, as shown below.)

   a.      list(range(5))
   b.      list(range(2, 7))
   c.      list(range(8, 11))
   d.      list(range(1, 10, 2))
   e.      list(range(9, 0, -3))
   f.       list(range(0, 9, -3))

2. The for loops below use an explicit list of numbers (e.g., [0, 1, 2, 3, 4]). Let’s say that we want to replace these explicit lists with expressions involving the range() function. What range()-function expression would be needed in each case? (Note: You do not need to include the list function in this case, because we only need the appropriate range expression to generate the necessary sequence of integers.)

   a. first for statement:

   for x in [0, 1, 2, 3]:
       print(x)
   

   b. second for statement:

   for x in [5, 6, 7]:
       print(x)
   

   c. third for statement:

   for x in [15, 11, 7, 3]:
       print(x)
   

Problem 8: Understanding loops

10 points; individual-only

1. Consider the following Python function, which uses an index-based for loop:

   def mystery(values):
        count = 0
        for i in range(len(values)):
            if values[i] < values[i-1]:
                count += 1
        return count
   

   Trace the execution of the following call to this function:

   mystery([4, 7, 3, 5, 8, 1])
   

   To do so, use the template that we have provided in section 8-1 of ps5pr678. In particular, you should:

   1. Complete the table to illustrate how the expression at the top of each column changes during the execution of the loop.

      The table begins with a row for the initial value of the variable count. Use the remaining rows to show what happens for each value of the loop variable i. You may not need all of the rows.

   2. Specify the return value of this function call in the space provided.

2. Consider the following Python program, which uses a while loop:

   a = 8
   b = 3
   print(a, b)
   
   while a > 2:
       a -= b
       b -= 1
       print(a - b)
   

   Complete the table that we have provided in section 8-2 of ps5pr678 to show how the variables change over time and the values that are printed. You may not need all of the rows.

Problem 9: Processing sequences with loops

30 points; pair-optional

This is one of only two problems in this assignment that you may complete with a partner. See the rules for working with a partner on pair-optional problems for details about how this type of collaboration must be structured.

Getting started

1. If you haven’t already done so, create a folder named ps5 for your work on this part of the assignment. You can find instructions for doing so here.

2. In Spyder, open a new editor window using File -> New File, and save it to your ps5 folder using the name ps5pr9.py.

1. Write a function sum_squares(vals) that takes as input a list of numbers vals and uses a loop to compute and return the sum of the squares of the individual numbers in the list. For example:

   >>> sum_squares([2, 5, 3])
   result: 38
   
   >>> sum_squares([1, 2, 3, 4])
   result: 30
   
   >>> sum_squares([6, 8])
   result: 100
   
   >>> sum_squares([])
   result: 0
   

   You solved a similar problem in Problem Set 2 using recursion, but for this problem set you must use a loop. You may not use recursion or a list comprehension.

   Here is a template that you can use to get started:

   def sum_squares(vals):
       """ your docstring goes here """
       total = 0
   
       for ____ in ______:
           ...
   

   Hint: This function should perform a cumulative computation that gradually builds up the sum of the squares of the numbers.

2. Write a function double(s, target) that takes as input an arbitrary string s and and a single-character string target, and that uses a loop to determine and return a new string in which all occurrences of target in s are doubled/repeated. For example:

   >>> double('program', 'r')
   result: 'prrogrram'
   
   >>> double('program', 'o')
   result: 'proogram'
   
   >>> double('banana', 'a')
   result: 'baanaanaa'
   

   You solved this problem using recursion in Problem Set 2, but for this problem set you must use a loop. You may not use recursion or a list comprehension.

   Here’s a template that you can use to get started:

   def double(s, target):
       """ your docstring goes here """
       result = ''
   
       for ____ in ______:
           ...
   

   Hint: This function should perform a cumulative computation that gradually builds up a string. We discussed a similar function (a loop-based remove_vowels) in Monday’s lecture.

3. Write a function process(vals, x) that takes as input a list of 0 or more integers vals and a single integer x, and that uses a loop to create and return a new list in which each element of the original list that is larger than x is replaced with a 0. For example:

   >>> process([5, 8, 3, 12], 6)
   result: [5, 0, 3, 0]
   
   >>> process([5, 8, 3, 12], 4)
   result: [0, 0, 3, 0]
   
   >>> process([5, 8, 3, 12], 15)
   result: [5, 8, 3, 12]
   
   >>> process([], 2)
   result: []
   

   You solved a similar problem in Problem Set 2 using recursion, but for this problem set you must use a loop. You may not use recursion or a list comprehension.

   Hint: This function should perform a cumulative computation that gradually builds up a list. We’ll write a similar function in this week’s lab.

4. Write a function diff(vals1, vals2) that takes as inputs two arbitrary lists of non-negative integers vals1 and vals2 and uses a loop to construct and return a new list in which each element is the the absolute value of the difference of the corresponding elements from the original lists. For example:

   >>> diff([3, 4, 2, 5], [7, 2, 9, 5])
   result: [4, 2, 7, 0]
   
   :::python
   >>> diff([5, 6, 2], [1, 9, 15])        
   result: [4, 3, 13]
   
   >>> diff([], [])        
   result: []
   

   If one of the lists is longer than the other, its “extra” elements – the ones with no counterparts in the shorter list – should appear immediately after the differences (if any) in the returned list. For example:

   >>> diff([0, 3, 6, 9], [1, 1])
   result: [1, 2, 6, 9]
   
   >>> diff([3, 1, 9], [2, 4, 5, 7])
   result: [1, 3, 4, 7])
   
   >>> diff([1, 2], [])
   result: [1, 2]
   
   >>> diff([], [3, 4, 5])
   result: [3, 4, 5]
   

   You solved a similar problem using recursion in Problem Set 2, but for this problem set you must use a loop. You may not use recursion or a list comprehension.

   Hints:

   • You will need to use an index-based loop so that you can access the corresponding elements from vals1 and vals2 at the same time. Here is a template that you can use to get started:

     def diff(vals1, vals2):
         """ your docstring goes here """
         result = []
     
         len_shorter = min(len(vals1), len(vals2))
         for i in range(len_shorter):
             ...
     

     Note that we determine the length of the shorter list before beginning the loop, because the loop should only consider the index values that are present in both lists.

   • After the loop, you will need to handle any “extra” numbers from the longer list (for cases in which the lists don’t have the same length). One way to do that is to use conditional execution (e.g., an if-else statement), although other approaches may also be possible.

Problem 10: Choosing the correct type of loop

14 points; individual-only

In Spyder, open a new editor window for your code, and save it to your ps5 folder using the name ps5pr10.py.

This problem is designed to give you practice in selecting the correct type of loop for a given problem.

1. Write a function get_even_val() that takes no inputs and that uses a loop to obtain an even integer from the user. More specifically, the function should perform the following tasks:

   • Get an initial integer value from the user using the input function and the prompt

     Enter an even integer:
     

   • If the user does not enter an even integer, keep asking for additional inputs until the user enters an even value. These additional inputs (if any) should use the following prompt:

     The input must be even. Try again:
     

   • Once the user enters an even value, return the value.

   You may assume that the user always enters an integer.

   For example:

   >>> get_even_val()
   Enter an even integer: 3
   The input must be even. Try again: -5
   The input must be even. Try again: 10
   result: 10
   

   Notes/hints:

   • The final line shown above displays the return value of the function. The function should not actually print this line; it should just return the appropriate value.

   • The function should use either a for loop or a while loop. You should decide which loop construct is the better one for this function, based on whether its task lends itself better to a definite loop or an indefinite loop.

   • Don’t forget that input always returns a string. As a result, you will need to use the int function to convert the input to an integer as discussed in lecture.

2. Write a function add_powers(m, n) that takes a positive integer m and an arbitrary integer n, and that uses a loop to add together the first m powers of n (from n**0 up to and including n**(m-1) power) and that returns the resulting sum.

   In addition, your function should also print a sequence of messages that describe the powers that are included in the sum. For example:

   >>> add_powers(4, 2)
   2 ** 0 = 1
   2 ** 1 = 2
   2 ** 2 = 4
   2 ** 3 = 8
   result: 15
   

   Notes/hints:

   • The final line shown above displays the return value of the function. The function should not actually print this line; it should just return the appropriate value.

   • The function should use either a for loop or a while loop. You should decide which loop construct is the better one for this function, based on whether its task lends itself better to a definite loop or an indefinite loop.

   • You will need an accumulator variable for the sum of the powers, which is the value that you will ultimately return. Don’t forget to initialize that variable before the start of the loop, and to update it within the loop.

   Here are some other examples:

   >>> add_powers(6, 3)
   3 ** 0 = 1
   3 ** 1 = 3
   3 ** 2 = 9
   3 ** 3 = 27
   3 ** 4 = 81
   3 ** 5 = 243
   result: 364
   
   >>> add_powers(3, -6)
   -6 ** 0 = 1
   -6 ** 1 = -6
   -6 ** 2 = 36
   result: 31
   

Submitting your work for Part II

Login to Gradescope by clicking the link in the left-hand navigation bar, and click on the box for CS 111.

You will make submissions to two separate assignments on Gradescope. The steps needed for the two submissions are different, so please make sure to follow carefully the procedures outlined below.

PS 5: Problems 6-8
Submit your ps5pr678.pdf file using these steps:

1. If you still need to create a PDF file, open your file on Google Drive, choose File->Download->PDF document, and save the PDF file on your machine.

2. Click on the name of the assignment in the list of assignments on Gradescope. You should see a pop-up window labeled Submit Assignment. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

3. Click the Select PDF button and find the PDF file that you created. Then click the Upload PDF button.

4. You should see a question outline along with thumbnails of the pages from your uploaded PDF. For each question in the outline:

   • Click the title of the question.
   • Click the page(s) on which your work for that question can be found.

   As you do so, click on the magnifying glass icon for each page and doublecheck that the pages that you see contain the work that you want us to grade.

5. Once you have assigned pages to all of the problems in the question outline, click the Submit button in the lower-right corner of the window. You should see a box saying that your submission was successful.

6. If needed, use the Resubmit button at the bottom of the page to resubmit your work.

PS 5: Problems 9 and 10
Submit your ps5pr9.py and ps5pr10.py files using these steps:

1. Click on the name of the assignment in the list of assignments. You should see a pop-up window with a box labeled DRAG & DROP. (If you don’t see it, click the Submit or Resubmit button at the bottom of the page.)

2. Add your files to the box labeled DRAG & DROP. You can either drag and drop the files from their folder into the box, or you can click on the box itself and browse for the files.

3. Click the Upload button.

4. You should see a box saying that your submission was successful. Click the (x) button to close that box.

5. The Autograder will perform some tests on your files. Once it is done, check the results to ensure that the tests were passed. If one or more of the tests did not pass, the name of that test will be in red, and there should be a message describing the failure. Based on those messages, make any necessary changes. Feel free to ask a staff member for help.

   Note: You will not see a complete Autograder score when you submit. That is because additional tests for at least some of the problems will be run later, after the final deadline for the submission has passed. For such problems, it is important to realize that passing all of the initial tests does not necessarily mean that you will ultimately get full credit on the problem. You should always run your own tests to convince yourself that the logic of your solutions is correct.

6. If needed, use the Resubmit button at the bottom of the page to resubmit your work. Important: Every time that you make a submission, you should submit all of the files for that Gradescope assignment, even if some of them have not changed since your last submission.

7. Near the top of the page, click on the box labeled Code. Then click on the name of each file to view its contents. Check to make sure that the files contain the code that you want us to grade.

Last updated on October 21, 2024.