Learn C++ through the learncpp.com curriculum — 345 lessons, auto-graded exercises, a sandboxed compiler, and an AI tutor that runs on your own API key.
cpproad turns the learncpp.com curriculum (34 chapters, 345 lessons) into an interactive course: read the lesson, write code in the browser, run it against real test cases, ask the tutor for a hint when you're stuck, and get the concept back tomorrow in review.
Free, open signup, no paid tier, no gated content.
| Layer | What runs it |
|---|---|
| App + API | Next.js App Router, TypeScript strict mode, Vercel |
| Data + auth | Supabase Postgres, magic-link auth, RLS on every table |
| Code execution | Judge0 on the RapidAPI shared host |
| Tutor | Gemini 2.5 Flash, streaming, user-supplied key |
Lesson summaries, exercises, and concept checks are authored offline and stored as plain
files under scripts/regenerated/v2/<lesson>/ — summary.md and exercises.json. They're
validated by scripts/validate_v2.ts and pushed into Postgres by scripts/push_v2.ts.
Serving a lesson is a database read. Nothing in the request path calls a model, so content is diffable in git, reviewable in a PR, and costs nothing per pageview. Content is paraphrased into cpproad's own voice, not scraped verbatim.
Bring your own Gemini key. It's AES-256-GCM encrypted before it reaches the database and
decrypted per request — cpproad never proxies a shared key, so tutor usage bills to the
person using it. Without a key, /api/chat returns 403 rather than falling back to
anything.
Hints escalate across four tiers: nudge → concept → structure → worked example. The tier comes from conversation state, so the tutor can't open with the answer.
Submissions compile and run in a sandboxed Judge0 instance, then get diffed against per-exercise test cases. Fork bombs, network egress, filesystem writes, OOM, infinite loops, and process enumeration were verified to fail closed as of 2026-06-11.
Production runs against RapidAPI's shared host, which means patch level, isolation, and rate
limits are outside our control. A self-hosted gVisor setup is staged in infra/judge0/ and
is not production-ready — the gVisor runtime is commented out and workers run
privileged. Re-harden before deploying it.
Every concept check a user answers writes both an attempt row and its scheduler state
(interval_index, next_due) in one RPC. GET /api/review/due returns up to 20 due cards
and nothing else touches the scheduler — all writes funnel through applyAttempt in
lib/content/review.ts so the two tables can't drift apart.
Connect a GitHub account and passed submissions get committed to your own public
cpproad-submissions repo via the Contents API, so practice shows up on your contribution
graph. Scope requested is public_repo; the token is encrypted at rest. Inert until an
operator registers an OAuth app.
Contributions are open, especially from people who want to teach: sharpen a lesson explanation, write a better exercise, fix a wrong test case, or flag where the curriculum glosses over a concept.
Every contribution starts with an issue. No unsolicited pull requests — open an issue, let it get triaged, then submit a PR referencing it. This keeps duplicate work down and means nobody burns a weekend on something already rejected or already in flight.
- Bug — open an issue with steps to reproduce.
- Wrong or unclear content — open an issue tagged
contentnaming the chapter and lesson number. The source files are underscripts/regenerated/v2/; fix them like any other file andscripts/validate_v2.tswill gate the merge. - Feature — describe the problem before the solution. Feature PRs without a prior issue get asked to open one.
This README documents what the project teaches and how it's put together, not how to run your own copy. Open an issue if you need a local setup guide.
MIT — see LICENSE.