Advent of Code 2025

C solutions for Advent of Code 2025 with automated input fetching and boilerplate generation.

Setup

Environment Variables

Create .env file in project root:

AOC_SESSION=your_session_cookie_here
AOC_YEAR=2025

Finding Session Cookie

1. Login to adventofcode.com
2. Open browser dev tools (F12)
3. Go to Application/Storage -> Cookies -> https://adventofcode.com
4. Copy value of session cookie
5. Paste into .env as AOC_SESSION

Usage

Build main executable:

make

Run a day (auto-generates + builds if needed):

./aoc <day>              # generate data/solution file, run tests + both parts
./aoc <day> --submit <part>  # submit answer for part 1 or 2

Structure

src/        Solution files (day1.c, day2.c, etc.) + utilities
inputs/     Puzzle input files (auto-fetched)
bin/        Compiled shared libraries (git-ignored)
build/      Object files (git-ignored)
scripts/    Generation and fetch automation

Workflow

1. ./aoc 1 - auto-generates src/day1.c, fetches input, builds, runs
2. Edit src/day1.c - implement part1()
3. ./aoc 1 - rebuild + run
4. ./aoc 1 --submit 1 - submit part 1 answer
5. Edit src/day1.c - implement part2()
6. ./aoc 1 --submit 2 - submit part 2 answer