Project 03 · Library Management System

Modules 13–15 (Weeks 13–15) · structs, vector, references, file persistence — the first stateful project Outcomes: CLO-6…CLO-8 (PF-13…PF-15). Difficulty: ★★★☆☆ · Builds on P2.

1. Problem description

A campus reading room lends books to members. The desk currently uses a paper register that is lost weekly. Write a console program that keeps a catalog of books and a register of which are out, saves state to a file between runs, and produces the desk's three daily reports. This is your first project whose data outlives the program: persistence changes design.

2. Learning objectives

Model records with a struct and manage a collection in std::vector.
Use references for in/out parameters where copies would lie.
Implement file round-tripping: load on start, save on change.
Apply the skip-and-report loader: malformed lines are data, not crashes.
Search by title (case-sensitive substring) and report by status.

3. Functional requirements

FR1 — Book record: struct Book { std::string title; std::string author; std::string id; bool out; std::string borrower; }; id is unique (B-1001 style); borrower is - when not out.
FR2 — On start, load catalog.txt (lines: id;title;author;out;borrower, out is 0/1). Print loaded: <n> skipped: <k> — skip reasons counted, never fatal. Missing file = empty catalog (not an error).
FR3 — Menu loop: add / lend / return / find / report / quit (exact words).
add: reads title, author; generates the next id (B-1001 + 1 per catalog length ever added — keep the counter in the file via a new max).
lend <id> <borrower>: marks out, records borrower; fails with not available if already out; no such id if absent.
return <id>: marks in, borrower back to -; no such id if absent.
find <text>: prints every title containing <text> (case-sensitive substring), id title out? lines; none if no hits.
report: counts line books: <n> out: <k> available: <m> then the out-list id -> borrower.
FR4 — Save the full catalog on quit (rewrite catalog.txt), and on every successful lend/return (crash tolerance — desk may lose power).
FR5 — quit is the only exit; EOF on stdin acts as quit (desk closes the terminal).

4. Non-functional requirements

NFR1 — Vector capacity grows by need; no fixed-size arrays anywhere.
NFR2 — All mutation flows through functions taking std::vector<Book>&; report functions take const std::vector<Book>&.
NFR3 — The save format and the load format are the same line grammar — a file your program wrote must load with skipped: 0.
NFR4 — Semicolons or commas only in the file; titles containing the separator are rejected at add time with title may not contain ';' (documented limitation, not silent corruption).
NFR5 — Compiles with the course contract, zero warnings; no raw new/delete anywhere.

5. Suggested data structures

std::vector<Book> catalog; — the single source of truth.
Next-id policy: scan for the current maximum numeric id on load; new id = max + 1 (survives deletions-in-file; state the rule in a comment).
Deliberately no classes yet: P4 introduces the invariant-carrying class; here the struct is honest data and the functions are the behavior.

6. User interaction design

loaded: 2 skipped: 1
menu (add|lend|return|find|report|quit): lend B-1001 Ali
ok
menu (add|lend|return|find|report|quit): report
books: 2 out: 1 available: 1
B-1001 -> Ali
menu (add|lend|return|find|report|quit): add
title: Dune
author: Herbert
added B-1003
menu (add|lend|return|find|report|quit): quit
saved: 3

7. Input validation requirements

VR1 — Load-time classes per line: wrong field count, bad out flag, or empty id → skipped (counted by class in a comment-documented tally).
VR2 — lend/return with unknown id: no such id, state unchanged.
VR3 — lend on an out book: not available, state unchanged.
VR4 — Empty title or author at add: bad text, book not added.
VR5 — File cannot be written on save: cannot save, exit 2 (data environment failure) — after printing the report of what would be lost.

8. Testing plan

#	Class	Scenario	Expected
T1	round-trip	add 2, quit, restart	`loaded: 2 skipped: 0`
T2	corrupt line	catalog with 1 bad line	`skipped: 1`, others load
T3	state machine	lend → lend same	second: `not available`
T4	state machine	return → return	second: `no such id` only if id absent; else ok→ok
T5	search	find `du` against Dune	hit; `find zz` → `none`
T6	id policy	add after max id B-1007	next is B-1008
T7	persistence	lend, kill program (EOF), restart	lend survived (saved on change)
T8	write-protect	read-only file/dir	`cannot save`, exit 2
T9	separator	title `A;B`	rejected, nothing added
T10	empty catalog	fresh file absent	`loaded: 0 skipped: 0`, reports all zero

9. Milestones

M1: struct + vector + load with skip-and-report + report + T2/T10.
M2: menu + add (id policy) + lend/return state machine + T3/T4/T6.
M3: save-on-quit + save-on-change + T1/T7/T8.
M4: find + hardening pass (VR4/VR5, T5/T9) + full test table.

10. Extension ideas ⚙

⚙ Due dates as day-numbers with an overdue report (arithmetic only).
⚙ find case-insensitive mode (tolower mapping — Module 11).
⚙ Two catalogs (books + members) with borrower ids resolved to names at report time — the join idea, two vectors.

11. Assessment rubric (10 points when graded as homework)

Points	Line
0–2	Load with skip-and-report; missing file handled (T2, T10)
0–2	State machine: lend/return invariants hold (T3, T4)
0–3	Persistence: round-trip, save-on-change, cannot-save path (T1, T7, T8)
0–2	Search + reports exact (T5, FR3 report line)
0–2	NFR1/NFR2/NFR5: vector+references, no raw pointers, contracts

Course-gate: does not compile with the contract → 0.

12. Student instructions

Work individually. Start from the file format — write a 3-line catalog.txt by hand and load it before writing any menu code. The skipped-counter and the round-trip test (T1) are the project's soul: a file you wrote must load clean. Deliverables: library.cpp, test_table.md (T1–T10), postmortem.md, and the sample catalog.txt you tested with. Zip as p03_<yourid>.zip. Use of new/delete or fixed-size arrays = scope violation under the scope-calibration line.