Cumulative Tests — CU1 and CU2

15 questions each · ~30 min each · everything so far is fair game — cumulative means the early material returns, mixed and combined · attempt ALL before any key · Hub · CU3–CU4 →

CU1 — Everything through loops (Weeks 1–6)

Q1. [Easy] The command that compiles lab.cpp with the course’s standard flags is…

a) cpp lab.cpp
b) g++ -std=c++17 -Wall -Wextra lab.cpp -o lab
c) g++ lab -o lab.cpp
d) run lab.cpp

Q2. [Easy] What does cout << 17 % 5; print?

a) 3
b) 2
c) 3.4
d) 85

Q3. [Easy] Which reads a whole line with spaces?

a) cin >> line;
b) getline(cin, line);
c) cin.getline(line);
d) read line;

Q4. [Easy] if (x = 5) — what is wrong?

a) nothing
b) assignment used where comparison was intended; x becomes 5 and the condition is truthy
c) x cannot be assigned in a condition
d) the else branch is required

Q5. [Medium] What does this print?

int x = 10;
if (x > 5) cout << "big";
if (x > 8) cout << "bigger";
if (x > 12) cout << "biggest";

a) big
b) bigbigger — two independent ifs both fire
c) bigbiggerbiggest
d) nothing

Q6. [Medium] What does this print?

int total = 0;
for (int i = 1; i <= 4; i++)
    total += i;
cout << total;

a) 4
b) 10
c) 6
d) 24

Q7. [Medium] What does this print?

int n = 6;
while (n > 0) {
    cout << n % 2;
    n /= 2;
}

a) 011 — binary of 6 printed least-significant first
b) 110
c) 6
d) infinite loop

Q8. [Medium] What does this print?

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 2; j++)
        cout << i << j << " ";
}

a) 00 01 10 11 20 21
b) 00 10 20 01 11 21
c) 00 01 02
d) 01 11 21

Q9. [Medium] This loop should read numbers until 0, but has a bug:

int x, sum = 0;
while (x != 0) {
    cin >> x;
    sum += x;
}
cout << sum;

The bug is…

a) sum is not initialized (it is)
b) x is tested before ever being set — uninitialized first test, and the sentinel 0 gets summed
c) the loop must be a for
d) sum should be a double

Q10. [Medium] What does this print?

int balance = 1000;
int withdraw = 300;
if (withdraw > 0 && withdraw <= balance)
    cout << "ok";
else
    cout << "denied";

a) ok
b) denied
c) okdenied
d) nothing

Q11. [Hard] What does this print?

int n = 4729;
int rev = 0;
while (n > 0) {
    rev = rev * 10 + n % 10;
    n /= 10;
}
cout << rev;

a) 4729
b) 9274
c) 22
d) 472

Q12. [Hard] What does this print?

for (int row = 1; row <= 3; row++) {
    for (int s = 0; s < 3 - row; s++) cout << " ";
    for (int star = 0; star < 2 * row - 1; star++) cout << "*";
    cout << "\n";
}

a) a centered pyramid — ` / * / **`
b) a left-aligned triangle
c) a solid block
d) nothing

Q13. [Hard] A program must keep asking for a mark until it lands in 0–100. The correct loop is…

a) do { cin >> m; } while (m < 0 || m > 100); — read, then repeat while invalid
b) while (m >= 0 && m <= 100) cin >> m;
c) for (int i = 0; i < 100; i++) cin >> m;
d) if (m < 0 || m > 100) cin >> m;

Q14. [Hard] What does this print?

int count = 0;
for (int i = 10; i <= 99; i++) {
    if (i % 7 == 0) count++;
}
cout << count;

a) 12
b) 13 — 14, 21, …, 98: thirteen multiples of 7
c) 14
d) 90

Q15. [Hard] The single most important habit when a loop misbehaves is…

a) rewriting it as a different loop type immediately
b) a trace table: variables as columns, passes as rows, update every cell honestly
c) adding more output inside the loop
d) deleting the loop

CU1 — Answer key

Q1 — b. The standard invocation: standard, warnings, source, -o name.

Q2 — b. 17 = 3·5 + 2 → remainder 2.

Q3 — b. getline reads the whole line; >> stops at whitespace.

Q4 — b. The classic = vs == slip: assignment succeeds (x becomes 5), its value 5 is truthy, the branch fires. Compilers warn; the habit is reading warnings as errors.

Q5 — b. Two independent ifs: 10 > 5 and 10 > 8 both true, 10 > 12 false. An else-if ladder would print only big.

Q6 — b. 1+2+3+4 = 10. The accumulator against a bounded for.

Q7 — a. Parity print + halve: 6%2=0 (n→3), 3%2=1 (n→1), 1%2=1 (n→0). Output 011 — 6 in binary is 110, printed in reverse. Binary decomposition is the digit-peel loop with base 2.

Q8 — a. Outer i runs 0–2, inner j runs 0–1 per pass, completing fully each time — row-major order.

Q9 — b. Two defects: the first test reads an uninitialized x (undefined), and even with luck, the 0 gets added to sum. The clean form tests the read itself: while (cin >> x && x != 0).

Q10 — a. 300 > 0 and 300 ≤ 1000 → both sides true → ok. The && guard is the withdrawal rule the bank labs enforce.

Q11 — b. The peel-and-rebuild: 9, then 7, then 2, then 4 → 9274. Reverse by arithmetic.

Q12 — a. Padding 3−row spaces then 2·row−1 stars per row — the centered pyramid. Dependent bounds both matter: one shapes position, the other width.

Q13 — a. Do-while fits: the first read must happen, then repetition continues exactly while the value is invalid. (b) tests m before it exists; (c) reads 100 times; (d) reads once.

Q14 — b. From 14 to 98 step 7: (98−14)/7 + 1 = 13. Counting multiples in a range by the endpoints — the closed form behind the loop.

Q15 — b. The trace table is the course’s universal loop debugger — slower than hope, correct more often. Output (c) is a fine supplement, but the table is what finds logic errors.

CU2 — Everything through collections (Weeks 1–9)

Q1. [Easy] Which is a valid array declaration with initialization?

a) int a[3] = {1, 2, 3};
b) int a[3] = 1 2 3;
c) array a = [1, 2, 3];
d) int[3] a = {1, 2, 3};

Q2. [Easy] vector<int> v; — which reports how many elements it holds?

a) v.length()
b) v.size()
c) sizeof(v)
d) v.count()

Q3. [Easy] A function receiving int a[] also receives int n because…

a) arrays cannot be looped otherwise
b) the array parameter decays to a pointer; size is not conveyed
c) n doubles as a return value
d) the compiler demands it

Q4. [Medium] What does this print?

int a[5] = {9, 4, 7, 1, 8};
int m = a[0];
for (int i = 1; i < 5; i++)
    if (a[i] < m) m = a[i];
cout << m;

a) 9
b) 1 — the min scan, seeded from the first element
c) 4
d) 29

Q5. [Medium] What does this print?

vector<int> v = {3, 6, 9};
for (int x : v) cout << x * 2;

a) 369
b) 61218 — the copy x doubled for output; v unchanged
c) 6 12 18
d) 3 6 9

Q6. [Medium] What does this print?

int a[4] = {5, 10, 15, 20};
cout << a[1] + a[3];

a) 25
b) 30
c) 15
d) 35

Q7. [Medium] What does this print?

vector<int> v;
for (int i = 0; i < 4; i++) v.push_back(i + 10);
cout << v.size() << ":" << v[2];

a) 4:12
b) 4:13
c) 3:12
d) 4:10

Q8. [Medium] What does this print?

int a[6] = {1, 2, 3, 4, 5, 6};
int count = 0;
for (int i = 0; i < 6; i++)
    if (a[i] % 3 == 0) count++;
cout << count;

a) 1
b) 2 — 3 and 6
c) 3
d) 6

Q9. [Medium] A marks array must report how many students scored above the average. The minimal structure is…

a) one pass: sum and count-above simultaneously
b) two passes: first sum → average, then count comparisons against it
c) sort, then count from the top
d) store marks in a string

Q10. [Medium] What does this print?

double avg(int a[], int n) {
    long long s = 0;
    for (int i = 0; i < n; i++) s += a[i];
    return (double)s / n;
}
int main() {
    int a[3] = {7, 8, 9};
    cout << avg(a, 3);
}

a) 8
b) 8.0? No setprecision — cout prints 8
c) 24
d) 7.5

Q11. [Hard] What does this print?

vector<int> v = {4, 1, 7, 2};
int best = 0;
for (size_t i = 1; i < v.size(); i++)
    if (v[i] > v[best]) best = i;
cout << best << "@" << v[best];

a) 2@7 — index tracking, then dereference at the end
b) 7@2
c) 0@4
d) 3@2

Q12. [Hard] What does this print?

int a[5] = {3, 1, 4, 1, 5};
for (int i = 0; i < 4; i++)
    if (a[i] > a[i + 1]) {
        int t = a[i]; a[i] = a[i + 1]; a[i + 1] = t;
    }
for (int i = 0; i < 5; i++) cout << a[i];

a) 13415 — one bubble pass: adjacent fixes only
b) 11345 — fully sorted
c) 31415
d) 51413

Q13. [Hard] What does this print?

int a[3][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
int s = 0;
for (int i = 0; i < 3; i++) s += a[i][i];
cout << s;

a) 15 — the main diagonal 1+5+9
b) 45
c) 12
d) 5

Q14. [Hard] What does this print?

vector<int> v = {5, 3, 8};
v[1] = v[0] + v[2];
for (size_t i = 0; i < v.size(); i++) cout << v[i];

a) 5138 — index write: slot 1 became 5+8
b) 538
c) 583
d) 1313

Q15. [Hard] A student’s marks analyzer prints the max but crashes for empty input. The missing guard is…

a) if (n == 0) { print "no data"; return; } — before any a[0] access
b) a bigger array
c) starting the loop at i = 0
d) using double instead of int

CU2 — Answer key

Q1 — a. Braced initialization fills elements in order.

Q2 — b. size() is the vector’s element count. sizeof returns bytes of the vector object, not its contents.

Q3 — b. Decay is the reason. The length parameter is the API convention built on that fact.

Q4 — b. Min scan — the max pattern with <. Seeding from a[0] keeps it correct for all-negative data.

Q5 — b. Range-for binds copies by default: x doubles for output, the vector’s elements untouched. int& x would have doubled the vector.

Q6 — b. a[1] = 10, a[3] = 20 → 30. Index arithmetic before sentiment.

Q7 — a. Pushed 10, 11, 12, 13 → size 4; index 2 is 12.

Q8 — b. 3 and 6 pass the % 3 test → 2.

Q9 — b. The average is unknown until the sum is — pass 1 computes it, pass 2 compares. Two passes exist because the data is stored; a streaming version cannot know the average mid-stream.

Q10 — b. The function returns 8.0; default cout formatting prints 8. Formatting is presentation — the value is what the function owns.

Q11 — a. best walks to index 2 (value 7); output pairs position@value. The index-as-artifact pattern.

Q12 — a. One bubble pass compares (3,1)→swap, (3,4)→ok, (4,1)→swap, (4,5)→ok → 1 3 1 4 5. One pass does not sort — it bubbles. The full sort needs n−1 passes; seeing one pass proves you understand the mechanism, not the slogan.

Q13 — a. The i == j identity selects the main diagonal: 1, 5, 9 → 15.

Q14 — a. v[1] = 5 + 8 = 13 → {5,13,8} printed without separators: 5138. Reads that look ambiguous (5138) are why the labs print separators.

Q15 — a. Empty input has no a[0] to seed from — the guard must precede every element access. Empty-collection handling is a first-class case in every analyzer from here to the capstone.

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