Exercises · T11 file handling

Covers: ifstream/ofstream, open modes, read-as-test loops, record round-trips, robust processing (skip-and-report), append, tokenizing file data. Lectures L29–L30. Outcomes PF-15.1–15.4.

10 exercises · ladder 🟢 → 🔴.

PF-E-122 · Write and Read Back Lines

Difficulty: Beginner · Lecture: L29 · Outcomes: PF-15.1 Prerequisites: E-079 Problem: Read 3 lines of text; write them to notes.txt (one per line, numbered inside the file as 1. … etc.). Reopen and print the file's contents. Verify (comment) what the file contains. Input: three lines · Output: the re-read file. Sample: input alpha beta → file line 1. alpha beta, echoed back. Hints: write, close (let scope do it), reopen — three phases.

PF-E-123 · Copy File (line by line)

Difficulty: Beginner · Lecture: L29 · Outcomes: PF-15.1 Prerequisites: E-122 Problem: Copy notes.txt (from E-122, or create it) to notes_copy.txt with the read-as-test getline loop. Print the number of lines copied. Handle the missing source with an error message and non-zero exit. Input: none · Output: copy confirmation + line count. Sample: — → copied 3 lines Hints: while (std::getline(in, line)) — never test eof() first.

PF-E-124 · Number File Statistics

Difficulty: Foundational · Lecture: L29 · Outcomes: PF-15.1, PF-15.2 Prerequisites: E-123 Problem: Read integers from numbers.txt (whitespace-separated, count unknown). Print count, sum, min, max, mean (2 decimals). Missing file → cannot open + exit 1. Empty file → print that report explicitly. Input: file · Output: five statistics (or messages). Sample: file 10 20 30 → count: 3 / mean: 20.00 Hints: seed min/max with the first successful read (L11's seeding lesson).

PF-E-125 · Append Diary with Timestamp Count

Difficulty: Foundational · Lecture: L29 · Outcomes: PF-15.1 Prerequisites: E-124 Problem: Read lines until an empty line; append each to diary.txt in append mode. Then report the total number of entries the file now holds (re-read and count). Demonstrate (comment) what would happen without std::ios::app. Input: lines until empty · Output: appended confirmation + total count. Sample: two new entries → appended: 2 / total entries now: 5 Hints: append mode preserves; plain output mode truncates — the L29 horror demo.

PF-E-126 · Student Record File Round-Trip

Difficulty: Foundational · Lecture: L29 · Outcomes: PF-15.2, PF-15.3 Prerequisites: E-125, E-113 Problem: Write n students (name, id, gpa) to students.txt as name id gpa lines; then load them back into a std::vector<Student> and print the roster with average GPA. State the format contract in a comment at both writer and reader. Input: n + records · Output: loaded roster + average. Sample: 2 students → roster lines + average gpa: 3.55 Hints: one record per line; the reader mirrors the writer field-for-field.

PF-E-127 · Skip-and-Report Loader

Difficulty: Intermediate · Lecture: L30 · Outcomes: PF-15.3, PF-15.4 Prerequisites: E-126 Problem: scores.txt contains lines like Ayesha,88 — but some lines are malformed (missing comma, non-numeric score, empty). Load with skip-and-report: print each bad line number with a reason, load the good ones, print final good/bad counts and the average of loaded scores. Input: file (create it from a provided pattern) · Output: per-line reports + summary. Sample: → line 2: skipped (no comma) / loaded 4, skipped 2 / average: 81.25 Hints: getline + istringstream per line (L30's separation trick).

PF-E-128 · Word Frequency from File

Difficulty: Intermediate · Lecture: L30 · Outcomes: PF-15.2, PF-11.4 Prerequisites: E-127 Problem: Read story.txt (several lines of lowercase words). Count word frequencies with parallel arrays (no map), print the top 3 words by count (ties: alphabetical) and the total word count. Input: file · Output: top-3 + total. Sample: → the: 12 / a: 9 / cat: 5 / total: 87 Hints: read with while (in >> word); reuse E-090's table logic per word.

PF-E-129 · Two-File Merge (sorted score files)

Difficulty: Intermediate · Lecture: L30 · Outcomes: PF-15.2, PF-9.4 Prerequisites: E-128 Problem: a.txt and b.txt each hold ascending integers (unknown counts). Merge into merged.txt preserving order without loading both fully into arrays — stream merge with two input streams (peek one value ahead per file). Input: two files · Output: merged.txt + line count printed. Sample: a = 1 4, b = 2 3 9 → merged 1 2 3 4 9 Hints: keep one pending value per stream; take the smaller; refill from that stream.

PF-E-130 · Config Reader with Defaults

Difficulty: Advanced Introductory · Lecture: L30 · Outcomes: PF-15.3, PF-15.4 Prerequisites: E-129 Problem: Read config.txt with lines key value (keys: theme, volume, difficulty). Unknown keys are skipped with a report; missing file or missing keys fall back to defaults (dark, 50, normal). Print the effective configuration and each anomaly found. Input: file (possibly missing/malformed) · Output: effective config + anomaly list. Sample: → theme=light / volume=50 (default) / anomaly: line 3 unknown key 'lang' Hints: per line: istringstream → key + value; a small if/else chain maps keys; track which keys were seen.

PF-E-131 · Transaction Log Audit

Difficulty: Advanced Introductory · Lecture: L30 · Outcomes: PF-15.3, PF-15.4, PF-14.4 Prerequisites: E-130 Problem: transactions.txt holds lines account action amount (action ∈ deposit, withdraw). Audit: apply valid transactions to a starting-balance table for 3 accounts (A101, A102, A103 — read initial balances first), skip-and-report malformed lines and overdrafts, then print each account's final balance, total processed amount, and anomaly count. Input: file + initial balances · Output: per-account report + anomaly count. Sample: → A101: 4500 (12 processed) / A102: 0 (overdraft attempt on line 7) / anomalies: 3 Hints: reuse E-118's deposit/withdraw logic over file records; the audit summary is the deliverable.