Year #3, Week #1 💻 ⚽️

New stuff we learned this week: 🤔

C: Preprocesser Directives

  • a preprocessor directive in C is any line beginning with #. Preprocessor directives are replaced before compilation.
  • an include statement is something like #include <stdio.h> or #include "../foo.c". You can think of it like an import statement in javascript, except that what is really going on under the hood is that the preprocessor copies and pastes the file right into that spot before compilation.
  • a #define directive (sometimes called “pound define”), creates a macro, which is like your own instruction to the preprocessor to copy paste the tokens following wherever it finds that macro. That means that the following C code:
#define MY_MAGIC_NUMBER 42
int x = 10 * MY_MAGIC_NUMBER;
  • actually gets replaced to become the below before compilation:
// blank line here now actually
int x = 10 * 42;

C: A Few Basic Types

  • The C language supports two categories of numeric types, integers and floating point numbers. There are several different sizes of each kind of number, but to get started we can just learn the two simplest: int and float.
  • int types hold positive or negative integers. Exactly how large depends on the machine and architecture and word-size of the computer you’re currently running on. But for most modern computers, an int is 4 bytes, or 32 bits, which means that they can store from -2,147,483,648 to +2,147,483,647.
  • to declare an int variable, you write:
int some_variable;
  • or, you can declare it and initialize it at the same time:
int my_age = 42;
  • if you never initialize your int variable, it will hold garbage, that is, whatever random bits might have happened to be in in that section of memory. 🗑
  • floats are similar to integers, except they can hold a decimal portion. When initializing or assigning a float value with a literal, it’s a good practice to include the character F after the literal:
int some_float;
some_float = 3.14F;
// [...]
int another_float = 7.7234F;
  • C has a character type: char, which holds a single character. A character in C is only 1 byte, which means there are only 256 total possible characters. This datatype was invented during the days of ASCII, when it was thought to be enough. For modern string processing, the char type is outdated and unusable for all but the simplest western languages.
  • You write a character literal with single quotes:
char my_char = 'a';
// or...
char another_char;
another_char = 'Z';
  • the sizeof operator in C returns an integer which is how many bytes that type takes on your machine:
sizeof(int); // 4
sizeof(char); // 1

Variables in C

  • Every variable in C is by default mutable, you can always change it’s value:
int age = 42;
age++;

char some_char = 'W';
some_char = 'A';
  • later versions of C added the const keyword, which allows you to declare that a variable cannot be re-assigned, much like declaring a variable with const in javascript. The compiler will error if you try to change it. The const keyword is technically a qualifier for the TYPE, so you put it before the type:
const int max_games = 10;
max_games = 100; //🚨 Compiler error
  • The type of a variable is only necessary when declaring a variable, and never should be indicated again.
int age = 42;

if (is_birthday) {
  // notice we don't write `int age...`
  age = age + 1;
}
  • That’s because you can’t change the TYPE of a variable in C:
int x = 9;
// [...later on...]
age = 'c'; // 🚨 ERROR, can't change from int to char

C: printf basics

  • printf() is like console.log() for C. It prints stuff to the terminal (technically, to standard out). The f stands for formatted because printf’s first argument is a format string which can have special placeholders that control the formatting of variables passed in the rest of the arguments.
printf("Hello, world!\n");
  • to use printf, you must include the stdio.h header with the #include <stdio.h> preprocessor directive.
  • printf is a variadic function that takes any number of arguments to replace placeholders in the first string, (called the format string).
    • %s for a “string” (char *)
    • %c for a charactater char
    • %d or %i for an int
    • %f for a float
int age = 42;
char x = 'x';
float pi = 3.13F;

printf("Age: %d, fav. char: %c, pi is %f\n", age, x, pi);
// prints > "Age 42, fav. char: x, pi is 3.14"

Make

  • to compile a c program, run cc <file>. This, by default, creates an executable binary file with the name a.out. If you want to customize the name of the output file, use the -o flag:
# creates a ./hello executable file
$ cc -o hello hello.c
  • the make utility originated as a unix utility program for compiling and building C programs. It can also make lots of other types of programs, and functions as sort of a general purpose scripting tool as well.
  • If you find yourself typing long commands to the c compiler, like clang -o foo foo.c -Wall -lcs50, you can simplify this using make.
  • what make does can be configured using a Makefile, but we won’t get into that until later. I have preconfigured make on the HTC pi to have some sensible defaults.

Homework Plan

  • Monkey Assignment #9
  • 1 days review all flashcards in your app.
  • 2 days touch typing practice
  • 1 day King C reading assignment (chapter 2)
  • 1 day King C exercizes (see below)
  • 1 day personal project
  • watch Lecture 1 of CS50 (from 21:52 to 57:30, till the “cookie break” 🍪)
  • 3 days Execute Program homework

    • King C Chapter 2 Programming Projects

    • First, make sure you’ve slowly and carefully read all of the New Stuff above ^^^.
    • Second, make sure you’ve slowly and carefully read all of chapter 2 of King C.
    • Third, make sure you’ve watched this week’s CS50 before working on this assignment.
    • SSH into the HTC pi, and create a new directory called king-c somewhere in your home dir.
    • Initialize it as an empty git repo.
    • Inside your repo dir, make another new directory called chapter-2. Inside that directory, create a file called hello.c that prints the message “Hello, world!” to standard out. Compile and run your program.
    • When you’ve got it working, make a commit. Make sure NOT to commit the compiled binary code. It should just be source code. Do this by either a) deleting the compiled binary, or b) creating a .gitignore file.
    • Create a brand new repository on GitLab called king-c. Once you’ve got it created, add it as a remote for the git repo you just made locally on the HTC pi.
    • push up your first commit with the “Hello world” C program.
    • Then, make a new branch called ch-2-projects.
    • Complete the following programming projects (not exercizes) from chapter 2: 1, 2, 3, 4, 5. Make a new file for every one, even number 3, which is a modification of number 2.
    • Extra Credit: ✨ Complete exercize 7.
    • Pick one of the exercizes that required user input, and switch from using scanf to using get_int() or get_float() from the cs50 library. You’ll have to include the cs50.h header file. For fun, try to compile this file without using make. How do you get rid of the error you see? They briefly showed how to do it before introducing make in the CS50 video.
    • commit your work, and push up a MR on GitLab, then slack me the URL.

    Personal Project Homework

    • Refer to your work plan you created a few weeks ago, and select the next item on your list. If you’re ahead or behind of where you thought you would be, make any modifications you think appropriate, then Slack me your goal for this week by WEDNESDAY at 9AM!!!! 📅 👋
    • Make sure you’ve addressed all of my feedback from last week, merge your MR, connect with vscode, pull from origin, and create a new branch.
    • Implement the feature or chunk of work you planned.
    • When you think you’re done, check things like:
      • did you leave in any console.log()s?
      • does it look good at all screen sizes?
      • do your storybook stories work and cover your components (if you’re using storybook)
      • are your components and variables named well?
      • is there anything you want to clean up, refactor, or DRY up before you submit?
    • when you’re happy with the code, build your site, submit a MR, and Slack both the URLs.
    • after I review, address any feedback I give you.

    Monkey #9 (Preparing the AST) 🐒

    • Address all feedback from prior MR’s, and merge.
    • Create a new branch.
    • Start at the beginning of section 2.6. The first few pages are not coding, but are very important information for understanding languages and interpreters, so read them carefully.
    • when you get to the section labelled Preparing the AST, that’s when you’ll start coding. Work through just that one section of coding work, ending when it changes to the next section, which is called Implementing the Pratt Parser.
    • Video link
    • Submit a MR, slack the MR url
    ← All homework