Monthly Archives: November 2018

Quitting Facebook

I quit Facebook last month.





An excerpt:







So how do you get your news?


So, ummm… yeah. I’m out.




Parsons Problem Lesson: quad_functions

Learning Programming is Hard

Many challenges face the new Computer Science learner. One of the most interesting times for students learning to program is that period after they’ve learned a new feature or programming strategy, but before they’ve had a chance to really master it. The syntax may still be unfamiliar, or the strategy is “the same, but different” as something that they’ve seen before.

A Parsons Puzzle

I first stumbled upon the “Parsons Problem” type of question in a paper by researchers Denny, Luxton-Reilly, and Simon, Evaluating a New Exam Question: Parsons Problems, published in 2008, which led me to Parsons and Haden’s original paper Parsons’ programming puzzles: a fun and effective learning tool for first programming courses.

A “Parson’s Puzzle” is a programming problem delivered via computer, in which code fragments, manipulated via a drag-and-drop interface, may be assembled to form a correct, working program. Clicking a “Check” button would provide some sort of feedback. Parsons and Haden proposed that the nature of the puzzle would improve engagement with the topic, provide better structure for students still struggling to understand fundamental logic, strategies, or algorithms, and even intentionally allow for common errors so that a student could get immediate feedback on fundamental misunderstandings.

Parsons and Haden’s original idea of helping to teach students with an automated system was adapted to a paper-based means of assessing students by Denny, Luxton-Reilly, and Simon. Along the same lines, it’s certainly possible to use a paper-based strategy of helping students develop and clarify their thinking on any given computer programming topic.

A Paper-Based Parsons Problem in the Classroom

In an introductory computer science course taught using Python, students had recently learned about functions, and had had the chance to learn how to use functions in several different contexts. Students were paired randomly and given a paper copy of the activity here [PDF], and asked to a) arrange the lines of code into strips of paper that they would assemble into a working version of the program, and then b) enter their code into the computer to verify that it works as intended.

This program solves quadratic equations using three functions:
* one function to get the coefficients a, b, and c
* one function to calculate the two roots, and
* one function to print out the results
@author You
@version 1.0

def get_coeffs():

def get_coeffs(a, b, c):

def calculate_roots(a,b,c):

def main():

def calculate_roots():

def display_solutions(root1, root2):

def display_solutions():


a, b, c = get_coeffs()

root1 = (-b + (b * b - 4 * a * c) ** (1/2)) / (2 * a)

root2 = (-b - (b * b - 4 * a * c) ** (1/2)) / (2 * a)

x, y, z = get_coeffs(a, b, c)

display_solutions(r1, r2)

return root1, root2


display_solutions(a, b, c)

print(root1, root2)

return a, b, c

print("The solutions are: ")

a = eval(input("Enter coefficient a: "))

b = eval(input("Enter coefficient b: "))

c = eval(input("Enter coefficient c: "))

r1, r2 = calculate_roots()

a, b, c = get_coeffs()

r1, r2 = calculate_roots(a, b, c)

if __name__ == "__main__":

#!/usr/bin/env python3


Students took the assignment seriously, and seemed to appreciate the nature of the puzzle, and the fact that all of the information was available to them—they just had to (literally) put the pieces together. There were some lively discussions—”Do we need a function header with parameters or not? Do we need the function to return a value or not?”—as well as a desire to get done with the puzzle-solving as quickly as possible in order to move onto entering the code into the computer to test their program.

For a larger assignment or project with many variations, the Parsons approach is not well-suited: there are too many variations that need to be considered. For students just learning to master a new topic, however—functions, conditionals, while-loops, for-loops, etc—the Parsons Problem strategy is a great way to build students’ skills and confidence in programming.


Paul Denny, Andrew Luxton-Reilly, and Beth Simon. 2008. Evaluating a new exam question: Parsons problems. In Proceedings of the Fourth international Workshop on Computing Education Research (ICER ’08). ACM, New York, NY, USA, 113-124.

Dale Parsons and Patricia Haden. 2006. Parson’s programming puzzles: a fun and effective learning tool for first programming courses. In Proceedings of the 8th Australasian Conference on Computing Education – Volume 52 (ACE ’06), Denise Tolhurst and Samuel Mann (Eds.), Vol. 52. Australian Computer Society, Inc., Darlinghurst, Australia, Australia, 157-163.

Demo: Encapsulation

The idea of encapsulation is fundamental to computers in a number of ways. Generally speaking, “encapsulation” refers to the idea of building a container around something, as if that thing were contained in a capsule. When it comes to computers, there are a couple of slightly different ways the term might be used.

Hiding code in a class, function, or library

Commonly in computer programming, encapsulation refers to the idea of hiding away the details of code. For example, you may write a bit of Python code that takes three coefficients for a quadratic equation a, b, and c, and calculates the real roots (solutions) of that equation:

a = 2
b = 4
c = -5
root1 = (-b + ((b * b) - (4 * a * c)) ** (1 / 2)) / (2 * a)
root2 = (-b - ((b * b) - (4 * a * c)) ** (1 / 2)) / (2 * a)

If you were having to write lots of programs to calculate quadratic roots, or if you wanted to be able to use those lines of code other places, you might very well write them into a small function or method called something like quadratic_solver that you could use in lots of different places. You might call that function like this:

roots = quadratic_solver(2, 4, -5)

In this single line of code, the messy details of multiplying, dividing, and square-rooting have all been hidden away from the main program. The details of that calculation have been “encapsulated” in the function.

Any time you import a library into your program–import java.util.Scanner; in Java, for example, or import random in Python–you are bringing in complicated bits of code that will be available for you to use without having to worry about some of the arcane, or mundane, or complex details that are contained in that code. The concept of encapsulation is extraordinarily powerful.

Programming languages: Machine code, Assembly, High-level

A second way of considering encapsulation is less obvious, but one that we use all the time.

High-level languages

You have almost certainly seen computer programs written in some “high-level” language like Python or Java. These languages are called high-level because they, for the most part, consists of syntax that might be recognized and understood.

Here’s a program that’s written in C, which adds up the numbers from 0 to 255 and prints out the result:

# include 

int main(void)
    int x, sum;
    sum = 0;
    x = 1;
    while (x < 256)
        printf("%d ",x);
        sum = sum + x;
        x = x + 1;
    printf("\nSum = %d\n", sum);

You may not understand everything in this program, but it certainly has a few English words in it, and even a programmer who doesn’t know C might be able to work their way through this program to identify how it works.

We have a serious problem, however. You may have heard that computers don’t understand English: they only work in binary digits, or “bits,” the zeroes and ones that are represented by a billion switches being turned “off” or “on.”

So how does the computer run this program?

It doesn’t. But there is another program on the computer–a compiler–that is able to take this program and convert it to something called Assembly Language.

Assembly Language

In Apple’s macOS, if you have the Developer Tools installed, you can use the gcc compiler in the Terminal to output a compiled version of the program.

$ gcc -o sum sum.c

What does this new version of the program look like? We can see the Assembly Language version by using the otool program:

$ otool -tv sum
(__TEXT,__text) section
0000000100000f10 pushq %rbp
0000000100000f11 movq %rsp, %rbp
0000000100000f14 subq $0x20, %rsp
0000000100000f18 movl $0x0, -0x4(%rbp)
0000000100000f1f movl $0x0, -0xc(%rbp)
0000000100000f26 movl $0x1, -0x8(%rbp)
0000000100000f2d cmpl $0x100, -0x8(%rbp)
0000000100000f34 jge 0x100000f65
0000000100000f3a leaq 0x65(%rip), %rdi
0000000100000f41 movl -0x8(%rbp), %esi
0000000100000f44 movb $0x0, %al
0000000100000f46 callq 0x100000f84
0000000100000f4b movl -0xc(%rbp), %esi
0000000100000f4e addl -0x8(%rbp), %esi
0000000100000f51 movl %esi, -0xc(%rbp)
0000000100000f54 movl -0x8(%rbp), %esi
0000000100000f57 addl $0x1, %esi
0000000100000f5a movl %esi, -0x8(%rbp)
0000000100000f5d movl %eax, -0x10(%rbp)
0000000100000f60 jmp 0x100000f2d
0000000100000f65 leaq 0x3e(%rip), %rdi
0000000100000f6c movl -0xc(%rbp), %esi
0000000100000f6f movb $0x0, %al
0000000100000f71 callq 0x100000f84
0000000100000f76 movl -0x4(%rbp), %esi
0000000100000f79 movl %eax, -0x14(%rbp)
0000000100000f7c movl %esi, %eax
0000000100000f7e addq $0x20, %rsp
0000000100000f82 popq %rbp
0000000100000f83 retq

This version of the program contains a series of commands–push, move, jump, add, call, pop, return–that manage the data in the program, addresses in memory (listed along the left side), and registers (like %esi). Some people program in assembly language, but you can see that it’s a much more complicated affair. The process of storing the value 1 in the variable x is, in assembly language

movl $0x1, -0x8(%rbp)

We can say that the assembly language instructions are “encapsulated,” or hidden away, so that we don’t have to worry about those implementation details. We can write our high-level code, and rest assured that the compilation process will take care of the dirty work for us.

Of course, we still haven’t gotten down to the 0s and 1s that the computer needs to run a program. Let’s go one step farther down.

Machine Language

In the process of compiling, we actually created a binary version of the program, with nothing but 0s and 1s. We can use the xxd program in the terminal to view that code:

$ xxd -b sum | cut -c 11-64
11001111 11111010 11101101 11111110 00000111 00000000
00000000 00000001 00000011 00000000 00000000 10000000
00000010 00000000 00000000 00000000 00001111 00000000
00000000 00000000 10110000 00000100 00000000 00000000
10000101 00000000 00100000 00000000 00000000 00000000
00000000 00000000 00011001 00000000 00000000 00000000
01001000 00000000 00000000 00000000 01011111 01011111
01010000 01000001 01000111 01000101 01011010 01000101
01010010 01001111 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000001 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00011001 00000000 00000000 00000000
11011000 00000001 00000000 00000000 01011111 01011111
01010100 01000101 01011000 01010100 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000001 00000000 00000000 00000000 00000000 00010000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00010000 00000000 00000000
00000000 00000000 00000000 00000000 00000111 00000000
00000000 00000000 00000101 00000000 00000000 00000000
00000101 00000000 00000000 00000000 00000000 00000000
00000000 00000000 01011111 01011111 01110100 01100101
01111000 01110100 00000000 00000000 00000000 00000000

It is this code–these 1s and 0s–encapsulated several layers below our original version, that the computer uses to run the program.

These 0s and 1s are used to operate the digital hardware, the memory locations and the logic gates, that produce a given output. In fact, before we had keyboards, mice, and monitors, the personal computer was simply a set of switches with lights above them. Computer code was entered using the individual switches–a long, painful, error-prone process–and output was read from the computer as a series of flashing lights.

Here’s a programmer entering a program by hand onto such a machine. The resulting program displays (in binary, of course!) the prime numbers between 2 and 255.

Fortunately, we don’t have to enter binary logic instructions by hand. Those codes are encapsulated well beneath our high-level languages.

Demo: Binary Numbers

If you teach Computer Science, chances are that learning about the binary numbering system is part of the curriculum at some point.

Why teach binary?

Some people question whether or not binary numbers should be part of a high-level curriculum, given the multiple layers of abstraction between, say, a webpage and the binary code that brings that page to life. I’d suggest that:

  1. Those multiple layers of abstraction / encapsulation are very much a part of computer science, and a perfect jumping off point for a conversation about binary numbers.
  2. Students should understand that binary numbers are at the heart of every computer. A great video for demonstrating how people used to have to program computers is this one, demonstrating the programming of an old 8080 microcomputer. Follow that up with a demo of high-level / assembly / binary version of a program, described here.
  3. Learning how to decipher a binary number is not that difficult, and provides students with a manageable gateway activity to the field of computer science.

Demonstration strategies

Binary numbers can certainly be displayed on a computer monitor or projected in front of the class. An interactive Python session works just fine:

>>> bin(13)
>>> print(bin(13))

A more visible and physical demonstration of binary numbers can easily be constructed using an outlet power strip, socket adapters, and low-wattage aquarium light bulbs (see parts list below).

This device can be easily manipulated at the front of the room, with individual bulbs easily turned on or off simply by screwing them in tightly (on), or unscrewing them slightly (off). Students can be asked to identify the decimal equivalent of a binary number, or asked to manipulate the bulbs themselves to produce the binary equivalent of a decimal number.


This inexpensive and physical, practical demonstration device can be used in the classroom, with parents, during open house events, etc. It has become a mainstay of every CS course I teach.

Parts List

Update your Creative Process

In early 2001, in press releases and ads, Apple encouraged its customers to Rip. Mix. Burn. their music on an iMac.

It was an audacious advertising campaign given that the recording industry was in the midst of grappling with the rampaging growth of digitally copied media via Napster, LimeWire, and others. The Mac would soon leverage its position as a media hub with the release of the iPod later that same year. The process of assembling a “mix tape” of songs for a friend would never be the same again… although that process has since disappeared completely. Because everybody just streams now.

This post isn’t about that, though.

If taking prerecorded media and putting it together into a custom mix was the “old creativity,” it didn’t take much in the way of actual… you know, creativity. Assembling and ordering someone else’s music is fine, but… it’s a stretch to call it creative.

Welcome to the new creative. “Rip. Mix. Burn.” has evolved.

Fork. Commit. Push.

That’s right, I’m talking about using GitHub to fork a project, make changes that you commit to your fork, and then push those changes back to the master. If you know about GitHub, this all makes perfect sense, and is absolutely reflective of a creative process happening.

And if you don’t know about GitHub? Well… you need to get on it!

More to come…