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📜 WAYPOINT LESSON

The capstone plan

⭐ beginner⏳ 12 min read📍 Lesson 82 of 85

Decompose the finance app into milestones — and learn which parts a stateless sandbox can grade.

The product

A personal finance ledger: record income and expenses, keep a running balance, and produce a monthly statement. The full build sequence:

  1. Model — a Transaction type: amount, category, description, date.
  2. Validate — an AddResult that explains rejected entries instead of throwing.
  3. Aggregate — running balance, category totals, month filtering.
  4. Report — a monthly statement: totals, biggest category, top entries.
  5. Persist — files (Module 14) and a project guide for assembling the real app locally.

Milestones 1–4 are graded here as pure functions over collections; milestone 5 exercises File/Path on disk in the challenges, and the project guide walks you through the full app with dotnet locally. Same domain, both worlds.