C++ Foundations — Exercises

24 items · attempt everything before the answer key · ← Module home

Save as eNN_description.cpp in your module folder (naming discipline); compile line for everything:

g++ -std=c++17 -Wall -Wextra eNN_description.cpp -o eNN

E1–E8 concept checks (written answers) · E9–E16 predict + code · E17–E24 code-it tasks. Answers for the odd concept checks and all predict items are in the collapsible key; code tasks are self-checked by compiling + the stated test.

Part A — concept checks (1–8)

E1. Name the four structural parts of a minimal C++ program, in order, one phrase each.

E2. What exactly does return 0; in main communicate, and to whom?

E3. Give one good reason to write a comment and one useless reason.

E4. Are total, Total, and TOTAL the same variable? What property of identifiers does this demonstrate?

E5. State the two identifier rules the compiler enforces, and two conventions this course enforces.

E6. Your teammate writes int x; then immediately std::cout << x;. What is wrong, what might print, and what is the course rule that prevents it?

E7. For each value, name its literal type: 42 · 42.0 · '4' · "42" · true.

E8. Why does the course say constants deserve UPPER_SNAKE_CASE? What two benefits does const give beyond naming?

Part B — predict and code (9–16)

E9 · e09_boxes.cpp. Predict, then write a program that: declares score initialized to 10, prints it, assigns 25, prints it, then adds 5 via score = score + 5, prints it. Were your predictions right?

E10 · e10_identifiers.cpp. Circle the illegal identifiers and state the rule broken: 2fast, my_score, for, Total, student count, _hide, passMark, class.

E11 · e11_rename.cpp. Rewrite this fragment with course-convention names (and say what each variable means):

int a = 7, b = 25;
int c = a * b;
std::cout << c;

E12 · e12_ints.cpp. Predict each output, then verify:

int a = 1000000;
std::cout << a * 3 << "\n";          // ?
std::cout << a * 3000 << "\n";       // ?  (!!)
long long b = 1000000LL * 3000;      // ?
std::cout << b << "\n";

E13 · e13_doubles.cpp. Predict, then verify: 7 / 2, 7 / 2.0, 7.0 / 2, 7 % 2, 7 % 2.0 (this last one won’t compile — why?).

E14 · e14_chars.cpp. Predict, then verify:

char c = 'C';
std::cout << c << "\n";        // ?
std::cout << c + 1 << "\n";    // ?
std::cout << static_cast<char>(c + 1) << "\n";   // ?

E15 · e15_bools.cpp. Predict, then verify:

bool a = true;
bool b = (3 > 7);
std::cout << a << "\n";        // ?
std::cout << b << "\n";        // ?
std::cout << a + b << "\n";    // ?

E16 · e16_strings.cpp. Write a program with firstName, lastName, printing: full name (concatenated with a space), its length, and the length of your first name alone. Then predict-and-check: what does firstName + 1 do? (Don’t fix it — just record the error message in your bug diary.)

Part C — code it (17–24)

E17 · e17_constants.cpp. A canteen charges TEA_PRICE = 15, COFFEE_PRICE = 40. Read cups of each (two ints) and print the bill line Tea x 2 : 30 style, plus total. No literal 15/40 anywhere except the constant definitions.

E18 · e18_literals.cpp. Write one statement per literal type (int, double, char, string, bool) printing each; then in a comment, write the type of the expression 'A' + 1 — and verify by printing it.

E19 · e19_moments.cpp. Demonstrate all three moments (declaration / initialization / assignment) with one variable level, including one deliberate read of a garbage variable in a comment (explaining what the compiler said when you tried).

E20 · e20_arith.cpp. Read two ints a, b (non-zero). Print all five: a + b, a - b, a * b, a / b, a % b — one per line, labelled. Then: what does a / b print for 7, 2? For −7, 2? Record both in the file’s comments.

E21 · e21_relations.cpp. Read marks (int). Print each comparison on its own line: marks >= 50, marks > 50, marks == 50, marks != 50. Then run with input 50 — how many lines print 1? Why exactly four?

E22 · e22_logic.cpp. Read an age and a y/n answer (has-ID, as in the Problem-Solving module). Print the two bools canEnter = (age >= 18 && hasID) and eligible = (age >= 18 || hasID) as 1/0. Test all four y/n × two ages (16, 20) — the 2×2 grid.

E23 · e23_incdec.cpp. Write the four-line experiment from Lesson 3 §3.4 (postfix a++ vs prefix ++c into new ints) from memory, predict all four outputs, then verify. Then add count += 3; and count -= 7; starting from 10, printing after each — predict first.

E24 · e24_cast.cpp. Read total and count (ints). Print the average three ways: total / count, static_cast<double>(total) / count, static_cast<double>(total / count). Run with 17 and 2; explain the three outputs in a comment. (This is Lesson 4’s crown-jewel exercise.)

Answers to selected exercises

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