C++ Foundations — Challenges

10 open problems · ★ think · ★★ sweat a little · ★★★ sleep on it · ← Module home

No solutions are published — by design. Each challenge lists what self-verification looks like: the tests or invariants that convince you (and a reviewer) it works. Keep every attempt; wrong versions with a diagnosis beat one magic correct version.

C1 ★ — Annotated autobiography. Write a program printing five lines about you, where every statement carries a comment explaining why it exists (not what it does). The verify step: hand it to a friend — can they reconstruct the output from comments alone?

C2 ★ — The constant catalogue. Take any Scenario 1–5 solution from the Problem-Solving module and convert every magic number into a named constant. Verify: changing PRICE_CHAI = 15 to 18 must alter exactly the outputs it should — and require zero other edits.

C3 ★ — Naming tournament. The same program written three times: once with names a, b, c, once with x1, x2, x3, once with proper course names. Then a comment block at the top: which version is checkable against the problem statement, and what made the difference? (The grade is the explanation, not the code.)

C4 ★★ — The honest calculator. Read two ints and print all four operations, but with the division done both ways (integer and decimal), each labelled. Verify with (7, 2), (−7, 2), (0, 5): your output must explain why the two divisions differ — in printed words, not just numbers.

C5 ★★ — Digit autopsy. Read one positive three-digit int. Using only / and %, print its hundreds, tens, and ones digits — one per line. Verify with 947 (→ 9, 4, 7) and the tricky pair 100 and 999; add 070 cases by trying 70 (a two-digit input — is that in your assumptions? document what happens).

C6 ★★ — Cast archaeology. Write one program printing the Lesson 4 trio for five different (total, count) pairs: total/count, static_cast<double>(total)/count, static_cast<double>(total/count). Verify: for every pair, output 2 and 3 must differ whenever total % count != 0 — and your comment block must say why in one sentence.

C7 ★★ — The accumulator race. Starting from x = 1, apply: x += 4; x *= 3; x -= 7; x /= 2; — predict on paper first. Then the challenge: find another sequence of compound operations with the same five operators that lands on the same final value, and prove both paths equal by printing after every step. Verify: both traces agree line by line.

C8 ★★★ — The overflow boundary. Find — by experiment, not by copying — the smallest positive int value v where v + v prints a negative number. Then explain (in comments) what the real boundary must be arithmetically, and why your experiment agrees or disagrees with the theory. Verify: long long arithmetic at your found value must NOT overflow — the pair of outputs is the proof.

C9 ★★★ — The self-documenting receipt. Rebuild the Problem-Solving module’s cafeteria bill (lesson) so that: every number is either input, a named constant, or a derived variable with a comment; the service-charge boundary is expressed with a constant SERVICE_THRESHOLD, not 500. Verify: the four test cases from the lesson pass unchanged, and swapping SERVICE_THRESHOLD to 600 changes only the boundary test’s outcomes.

C10 ★★★ — Teach the bug. Choose three of Lesson 4’s mistake gallery (M1–M8). For each: write a program containing the mistake, record the actual (wrong) output or compile error, then write the corrected version in the same file (guarded by comments), and a one-sentence lesson in your bug diary. Verify: a classmate reads only your wrong output and your sentence — and can state the fix.

How challenges are “graded”

Record all ten in your bug diary / LAB-NOTES; the Capstone rubric’s polish line starts here — habits, not heroics.

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