Setting up a MacBook Air for C

1 · Open the terminal, and learn five commands

Press ⌘+Space, type Terminal, press Return. You get a window with a prompt ending in % — it's waiting for a command. Drag Terminal to the Dock; you'll open it every study session. Five commands cover 95% of what this course needs:

Two habits that make the terminal pleasant instead of painful: press Tab to auto-complete a file or folder name (type cd la, hit Tab, get cd lab01/), and press ↑ to bring back the previous command instead of retyping it. Make a home for the course now:

% mkdir -p ~/cs-u111/lab01
% cd ~/cs-u111/lab01
% pwd
/Users/yourname/cs-u111/lab01

(~ means your home folder. One folder per lab keeps submissions from getting mixed up.)

2 · Install the compiler — one command, then wait

Apple bundles a C compiler in the Command Line Tools. Ask for them:

% xcode-select --install

A dialog pops up; click Install, agree, and wait — it's a 1–2 GB download, typically 10–20 minutes on hostel Wi-Fi. If instead you see command line tools are already installed, you're done already. When it finishes, verify:

% clang --version
Apple clang version 17.0.0 (the numbers will differ — any version is fine)
% gcc --version
Apple clang version 17.0.0 (yes, the same thing — see below)

3 · An editor: VS Code, kept simple

You can write C in any plain-text editor, but a programmer's editor colours the code and points at mistakes as you type. The standard choice is Visual Studio Code — free, from code.visualstudio.com (choose the Apple Silicon build if asked; the site usually detects it). Then:

1. Open VS Code → Extensions (the blocks icon on the left, or ⇧⌘X) → search C/C++ → install the one by Microsoft. That's the only extension you need.
2. File → Open Folder… → pick cs-u111. Always open the folder, not a single file — then the file tree on the left shows every lab.
3. Optional but worth it: ⇧⌘P → type shell command → "Install 'code' command in PATH". Now code . in the terminal opens the current folder in VS Code.

Skip "Code Runner"-type extensions and the green run button for now. The lab exam is at a terminal; get comfortable compiling from the terminal first, so nothing about the lab feels foreign. VS Code has a built-in terminal (⌃`) that is the same Terminal — use whichever.

4 · The first program, and the loop you'll run all semester

In VS Code, create a new file inside lab01 called hello.c (the .c matters — it tells the editor and compiler it's C). Type this in — type it, don't paste, so your fingers learn the shape:

#include <stdio.h>

int main(void)
{
    printf("Hello from my Mac!\n");
    return 0;
}

Save (⌘S). Now in the terminal, inside lab01:

% gcc -Wall -Wextra -std=c11 -o hello hello.c
% ./hello
Hello from my Mac!

Read the first command word by word, because you'll type it hundreds of times: gcc — the compiler. -Wall -Wextra — "warn me about everything suspicious" (more on that in a moment). -std=c11 — use the modern C standard the textbook uses. -o hello — name the output program hello. hello.c — the file to compile. The second command, ./hello, runs the program; the ./ means "the one in this folder".

That's the whole loop, and it never changes:

Warnings are errors that haven't happened yet

With -Wall -Wextra the compiler will sometimes produce a warning and still build the program. Treat every warning as a bug to fix before running — "variable used before it's set", "comparison is always true", "unused variable" are exactly the mistakes that cost lab marks. A clean compile means no output at all from the gcc line. Some instructors compile with -Werror (warnings become errors); adding it yourself is a good habit.

Programs that read input

Most lab programs read numbers from the keyboard. Try one:

#include <stdio.h>

int main(void)
{
    int n;
    printf("Enter a number: ");
    scanf("%d", &n);
    printf("Double is %d\n", 2 * n);
    return 0;
}

% gcc -Wall -Wextra -std=c11 -o double double.c
% ./double
Enter a number: 21
Double is 42

Two keys to know before your first infinite loop: ⌃C kills a program that won't stop; ⌃D tells a program that's waiting for input that there is no more (this is "end of file" — the file-handling chapter will make it matter).

5 · Where a Mac differs from the lab machines

The lab almost certainly runs Linux with GNU gcc (the handout doesn't say — confirm in the first lab and this page will be adjusted). Standard C is standard C, so your programs move across unchanged. The differences that actually bite:

6 · A five-minute daily warm-up, once labs start

Open Terminal, cd to the current lab folder, and retype one short program from the last lecture from memory — compile, run, fix. It's the programming equivalent of the maths daily drill: it makes the mechanics automatic (headers, main, semicolons, braces, the compile line), so lab time goes to the actual problem. The 65% of this course that's written on paper, closed book, is precisely a test of whether those mechanics are automatic.