Introduction: The Cartesian Dream Of C

Whatever I have up till now accepted as most true and assured I have gotten either from the senses or through the senses. But from time to time I have found that the senses deceive, and it is prudent never to trust completely those who have deceived us even once.

—Rene Descartes, Meditations On First Philosophy

If there ever were a quote that described programming with C, it would be this. To many programmers, this makes C scary and evil. It is the Devil, Satan, the trickster Loki come to destroy your productivity with his seductive talk of pointers and direct access to the machine. Then, once this computational Lucifer has you hooked, he destroys your world with the evil "segfault" and laughs as he reveals the trickery in your bargain with him.

But, C is not to blame for this state of affairs. No my friends, your computer and the Operating System controlling it are the real tricksters. They conspire to hide their true inner workings from you so that you can never really know what is going on. The C programming language's only failing is giving you access to what is really there, and telling you the cold hard raw truth. C gives you the red pill. C pulls the curtain back to show you the wizard. C is truth.

Why use C then if it's so dangerous? Because C gives you power over the false reality of abstraction and liberates you from stupidity.

What You Will Learn

The purpose of this book is to get you strong enough in C that you'll be able to write your own software in it, or modify someone else's code. At the end of the book we actually take code from a more famous book called K&R C and code review it using what you've learned. To get to this stage you'll have to learn a few things:

  • The basics of C syntax and idioms.
  • Compilation, make files, linkers.
  • Finding bugs and preventing them.
  • Defensive coding practices.
  • Breaking C code.
  • Writing basic Unix systems software.

By the final chapter you will have more than enough ammunition to tackle basic systems software, libraries, and other smaller projects.

How To Read This Book

This book is intended for programmers who have learned at least one other programming language. I refer you to Learn Python The Hard Way if you haven't learned a programming language yet. This book is meant for total beginners and works very well as a first book on programming. Once you've done those then you can come back and start this book.

For those who've already learned to code, this book may seem strange at first. It's not like other books where you read paragraph after paragraph of prose and then type in a bit of code here and there. Instead I have you coding right away and then I explain what you just did. This works better because it's easier to explain something you've already experienced.

Because of this structure, there are a few rules you must follow in this book:

  • Type in all of the code. Do not copy-paste!
  • Type the code in exactly, even the comments.
  • Get it to run and make sure it prints the same output.
  • If there are bugs fix them.
  • Do the extra credit but it's alright to skip ones you can't figure out.
  • Always try to figure it out first before trying to get help.

If you follow these rules, do everything in the book, and still can't code C then you at least tried. It's not for everyone, but the act of trying will make you a better programmer.

The Core Competencies

I'm going to guess that you come from a language for weaklings. One of those "usable" languages that lets you get away with sloppy thinking and half-assed hackery like Python or Ruby. Or, maybe you use a language like Lisp that pretends the computer is some purely functional fantasy land with padded walls for little babies. Maybe you've learned Prolog and you think the entire world should just be a database that you walk around in looking for clues. Even worse, I'm betting you've been using an IDE, so your brain is riddled with memory holes and you can't even type out an entire function's name without hitting CTRL-SPACE every 3 characters you type.

No matter what your background, you are probably bad at four skills:

Reading And Writing
This is especially true if you use an IDE, but generally I find programmers do too much "skimming" and have problems reading for comprehension. They'll skim code they need to understand in detail and think they understand it when they really don't. Other languages provide tools that also let them avoid actually writing any code, so when faced with a language like C they break down. Simplest thing to do is just understand everyone has this problem, and you can fix it by forcing yourself to slow down and be meticulous about your reading and writing. At first it'll feel painful and annoying, but take frequent breaks, and then eventually it'll be easy to do.
Attention To Detail
Everyone is bad at this, and it's the biggest cause of bad software. Other languages let you get away with not paying attention, but C demands your full attention because it is right in the machine and the machine is very picky. With C there is no "kind of similar" or "close enough", so you need to pay attention. Double check your work. Assume everything you write is wrong until you prove it's right.
Spotting Differences
A key problem people from other languages have is their brain has been trained to spot differences in that language, not in C. When you compare code you've written to my exercise code your eyes will jump right over characters you think don't matter or that aren't familiar. I'll be giving you strategies that force you to see your mistakes, but keep in mind that if your code is not exactly like the code in this book it is wrong.
Planning And Debugging
I love other easier languages because I can just hang out. I type the ideas I have into their interpreter and see results immediately. They're great for just hacking out ideas, but have you noticed that if you keep doing "hack until it works" eventually nothing works? C is harder on you because it requires you to plan out what you'll create first. Sure, you can hack for a bit, but you have to get serious much earlier in C than other languages. I'll be teaching you ways to plan out key parts of your program before you start coding, and this will hopefully make you a better programmer at the same time. Even just a little planning can smooth things out down the road.

Learning C makes you a better programmer because you are forced to deal with these issues earlier and more frequently. You can't be sloppy and half-assed about what you write or nothing will work. The advantage of C is it's a simple language you can figure out on your own, which makes it a great language for learning about the machine and getting stronger in these core programmer skills.

C is harder than some other languages, but that's only because C's not hiding things from you that those other languages try and fail to obfuscate.


This book is free for you to read, but until I'm done you can't distribute it or modify it. I need to make sure that unfinished copies of it do not get out and mess up a student on accident.