Josh Davis

I'm currently an Engineer working at Amazon and am living in Seattle.

I like to learn, pet kittens, and wear fluffy socks.

I never save anything for the swim back.

24 July 2013

C: A Minute to Learn… A Lifetime to Master

Last weekend I picked up the book Expert C Programming: Deep C Secrets from a local bookstore here in Seattle. The C Programming language has arguably been the most influential programming language that I have learned. It was the first language that I grew to love and Expert C Programming inspired me to write up this short post chronicling my journey learning C, some resources that I find valuable, as well as various other things.

K&R: Know Your Roots

I read the famous K&R book back in high school during a blissful week at the beginning of spring one year. I fell in love with the C programming language. My views match up pretty well with what most of the community already knows: it is one of the most beautifully written introductions to a programming language ever. The most striking part is that the first edition it came in at only 228 pages.

Trivia Tidbits

  • The K&R book popularized the standard of having one’s first program write “Hello, world.
  • The K&R book also popularized its own brace style, which then influenced the brace style used in the Unix and Linux kernels.

What Made it so Great?

Considering I read it so long ago, it’s hard for me to determine why it made such an impact on me. It might possibly have been the succinctness of it. Being able to learn a language after reading ~200 pages allows one to program more which was how I learned the best back in high school.

I also think a big part of it had to do with the examples in the book. Some of the examples included converting an int to a binary/hexadecimal string, writing a function that takes in strings of numbers written in scientific notation and returning a float. My personal favorite was one of the exercises from the first chapter:

Write a program to check a C program for rudimentary syntax errors like unbalanced parentheses, brackets and braces. Don’t forget about quotes, both single and double, escape sequences, and comments.

A full list of the exercises by chapter (as well as the solutions) can be found on the clc-wiki. If you actually want to try and solve them, don’t cheat and look at the solutions!

Dive Deep

Now back to the book that inspired me to write this post. Expert C Programming covered some of the less well-defined parts of C.

Declarations

It had a chapter just on C declarations and how to read them. If you spend any amount of time programming C at all, you’ve more than likely come to realize that sometimes determining what a variable is defined as is quite a difficulty.

The book has a short set of rules to follow to decipher a declaration yourself. It also provides a small little program that will do the deciphering for you. If you put in a declaration, it will output the English equivalent.

One of the best resources out there appears to be this online C declaration to English parser that will do the work for you. However, if you want to be able to do this without relying on a website, definitely check out this guide.

Arrays vs Pointers

Often a person will think that a pointer and an array are the same thing because of the following:

int a[] = {0, 1, 2, 3, 4};
int *p;

p = a;

if (a[2] == p[2]) {
    printf("Equal\n");
}

Running the above in a main function will print out Equal and stop. The chapter goes more in depth on why they aren’t the same with more examples.

The general idea is that a actually holds the data while p is holding the location of where a is at. This means that p[2] can’t just access it at once, it must dereference the pointer to find out where a is stored, then calculate the offset. While a[2] can calculate the offset immediately.

History Lesson

The book also has a ton of little stories about certain parts of the C language. For example it discusses how C came to have so many different ways to increment an integer. The i++ and ++i came about because it was a single machine instruction for the PDP-11.

That’s just one example but the book was written in 1994 so it is packed with other little history facts that make it really interesting.

I Guess I’m an Expert Now

There are 11 chapters all together and each one looks at a crucial aspect of C that might be a bit fuzzy. I definitely recommend checking it out if you like C. I think it also would make a great reference book for when you get stuck on a certain feature, say like declarations or pointers.

Learning by Doing

It certainly goes without saying that writing a lot of code will help you to learn the language. I certainly did this with C when I was learning it.

In addition to most of the exercises in K&R, I also did a lot of the Project Euler problems in C. Project Euler is just a list of problems that intersect math and programming. Most often the problems can be solved using brute force, but designing a better algorithm or understanding the problem more usually can lead to a better solution.

My favorite part about Project Euler is that the only thing that it is very easy to check if you are right or wrong. All the problems have a single number as the result. Take the first problem for example:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

The end result is just the sum; it doesn’t matter how long it took to calculate or what language you use. This makes it easy to experiment and work on solving it first before optimizing a solution.

A repository that I came across recently has been trending on GitHub for the last few days. The list of projects originally came from Martyr2 on dream-in-code, but it is a repository of a guy that is trying to implement most of the list in Python.

Learning by Reading

There’s a certain point where you can only learn so much from writing code. One of the best ways to pick up new programming habits or techniques is best achieved by reading other people’s code.

C is so ancient that there are a ton of projects out there that you can use to read. Here are a few of my favorites:

  • Plan 9 source code. Plan 9 is an OS that was developed back in the early 90s. It uses a dialect of ANSI C so it shouldn’t be too foreign.
  • dlmalloc. dlmalloc stands for “Doug Lea malloc” and is a reimplementation of malloc. It has a few benefits as well as a few shortcomings.

Conclusion

Like the title says, the C programming language can be really simple to learn at first. Yet like Reversi, the flexibility of the language allows for complexity to manifest itself. Mastering the language can take a very long time.

Since the language is so low level, it is very tightly dependent on the implementation and hardware it is running on. Although the C standards are supposed to limit these edge cases, they still exist.

I just read an article earlier today about what happens when malloc(0) is called. As it turns out, it depends on the system what malloc(0) will return.

C might seem quite scary considering it has been out for so long yet people still have a ton of issues with it. I don’t see it that way though.

Instead C is much like the game of chess, except the other player is the computer. The more you master C the better you will get at countering the computer and bending it to your will. It now becomes a game of mathematical precision and a direct test of your knowledge of C and the computer.

It’s certainly more magical and beautiful this way.

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