Category Archives: CS101

Programming basics.

The Eight Queens

23 Sunday Jun 2019

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There’s a fairly simple puzzle, called The Eight Queens, that I’ve long favored as a project for first semester CS students. The problem is simple enough for a beginner to tackle, yet also interesting enough to be engaging. (And just tricky enough to be a nice beginner challenge.)

Due to a discussion on my other blog, I dug out an old Python implementation I had, and, after looking at it, I thought it might be worth writing a post about. If nothing else, as I said, the problem is interesting enough to be engaging.

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Full Adder Sim V2.0

08 Wednesday May 2019

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This is the third post in the Full Adder series. The first post explored ways to code the abstract model of a full-adder. The second post explored one way to code a simulation of a physical system (where the models are of the components of the system).

This post explores another gate-based model, but one with only one type of gate. This simulation is close to being transistor-level.

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Full Adder Simulation

07 Tuesday May 2019

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In the last post, I explored different ways to model the logic of a full-adder. In this post I’ll explore a model of a physical instance of a full-adder — a model that simulates physical reality.

Because a full-adder is, at root, a mathematical expression, various software models can accomplish the same results. Models are abstractions, so the only thing a model can simulate perfectly is another model.

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Full Adder Code

05 Sunday May 2019

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I was involved in a debate recently about whether a full adder logic circuit is a computer. The computer science answer is: “No, not as we define a computer.”

I plan to address that answer in detail on my main blog. Here I wanted to show some of the different ways a full adder can be modeled and implemented.

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Iteration versus Recursion

19 Monday Dec 2016

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When it comes to what makes a computer (or any other) language a programming language, there are three characteristics usually required:

  1. Saving state (variables)
  2. Selecting a code path (if-then)
  3. Iteration or recursion (or equivalent)

This post is just a brief note (for a friend) about the third item and why it allows three distinct options.

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The Thing About Constants

16 Tuesday Aug 2016

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Along with “always use less-than” is another great piece of always advice, except this one is a prohibition, a never rather than an always (same thing, really, from a programmer’s point of view).

It has to do with never having literal values embedded in your code!

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Counting From Zero

08 Monday Aug 2016

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In his brief 1982 essay (EWD831), computer science giant Edsger Dijkstra examines a topic that (inappropriately, as it turns out) vexes some programmers: Why in the world do computer people count starting at zero? Everyone knows that counting starts at one!

As it turns out, there are two very good reasons for counting from zero!

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State Engines, part 3

25 Wednesday Nov 2015

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In the first two parts of this series I’ve introduced state engines and taken apart a specific instance of an engine. Now it’s time to tie together the design idea with approaches to building a variety of such engines.

Because the programming logic is in the state table, the engine can be fairly generic. That means it’s possible to create a state engine framework you can reuse for a variety of applications.

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