# Mid-semester examination: sample questions ## Six question types, one worked sample of each **Instructor:** [Dr. Debasish Pattanayak](https://drdebmath.github.io)

## The paper has six sections | Section | Type | Marks | What you write | | --- | --- | --- | --- | | A | True or false | 10 | The verdict **and** a one-line reason naming the C++ rule | | B | Match the concepts | 10 | The letter from Column B for each term in Column A | | C | Complete the code | 20 | Only the missing fragment in each numbered blank | | D | Does it compile, and what happens? | 10 | **Y** or **N**, and if it compiles: the exact output, *infinite loop*, or *stops with an exception* | | E | Determine the output or final value | 10 | The exact value or output | | F | Bonus trivia | 10 | A short answer; counts towards the total, but the paper is capped at 60 | Two hours. Assume C++17, all needed headers present, valid input. The samples below are **not** on the paper; each one shows the format and what a full-marks answer looks like.

## Section A sample · True or false, with a reason "A <code>for</code> loop whose condition is false the first time it is tested still runs its body once." <ol class="course-quiz-options"> <li><button class="course-quiz-option" type="button">True</button></li> <li><button class="course-quiz-option" type="button" data-course-quiz-correct>False</button></li> </ol> <p class="course-quiz-explanation"><strong>False</strong> — a <code>for</code> loop tests its condition <em>before</em> every pass, including the first, so a false condition means zero passes. Only <code>do-while</code> runs its body before testing.</p> The reason carries the mark. "False, it does not work like that" earns nothing; name the rule.

## Section B sample · Match the concepts | | Column A | | Column B | | --- | --- | --- | --- | | 1 | `std::size_t` | A | Reads one whitespace-separated token | | 2 | Sentinel value | B | Unsigned type returned by `size()` | | 3 | `std::cin >>` | C | Input value that means "stop", never treated as data | | 4 | Loop invariant | D | Statement that stays true after every iteration | **Answers:** 1 = B, 2 = C, 3 = A, 4 = D Every description in Column B is used exactly once, so a doubtful pair can be settled by elimination after the certain ones are placed.

## Section C sample · Complete the code *`countAbove` must return how many elements of `a` are strictly greater than `limit`. `main` prints that count followed by a newline and returns the value that signals success.* ~~~cpp int countAbove(const array<int,4>& a, int limit) { int count = 0; for (int value : a) { if (______________) { // 1 ______________; // 2 } } return ______________; // 3 } int main() { array<int,4> a{3, 9, 12, 5}; cout << countAbove(______________) << '\n'; // 4 return ______________; // 5 } ~~~ **Expected output, exactly:** `2` followed by a newline. **Blanks:** 1 `value > limit` · 2 `++count` · 3 `count` · 4 `a, 8` (any limit that leaves 9 and 12 above it and 3 and 5 below) · 5 `0`

## Section D sample · Does it compile, and what happens? Each snippet sits inside `main` with the headers present. Write **Y** or **N**; if it compiles, also write what happens. | | Snippet | Compiles | Then | | --- | --- | --- | --- | | 1 | `int k = 3; k++; cout << k;` | **Y** | `4` | | 2 | `double d = 2.5; switch (d) { case 2: break; }` | **N** | `switch` needs an integral value | | 3 | `vector<int> v{7}; cout << v.at(1);` | **Y** | stops with an exception: `at(1)` on a one-element vector | | 4 | `int i = 0; while (i < 3) { cout << i; }` | **Y** | infinite loop printing `0` | Both parts must be right for the mark: **Y** alone, or the right output with the wrong verdict, earns nothing.

## Section E sample · Determine the output or final value ~~~cpp int a = 4; int b = a++ * 2; // b = ? ~~~ ~~~cpp int f(int n) { if (n == 1) return 1; return n + f(n - 1); } // f(4) = ? ~~~ ~~~cpp string s = "programming"; cout << s.substr(3, 4); // prints ? ~~~ **Answers:** `b` = 8 and `a` = 5 (postfix hands back the old value, then increments) · `f(4)` = 10 · prints `gram` Write exactly what the program produces: `8`, not "eight"; `gram` with no quotes and no extra spaces.

## Section F sample · Bonus trivia "Which mathematician's name is on the machine model that every modern computer is compared against, proposed in 1936?" **Answer:** Alan Turing (the Turing machine). Ten such questions, one mark each. They are added to your total, but the paper is recorded out of 60: a total above 60 counts as 60. Answer them last.

## How to spend the two hours 1. **Sections A, B and E first** (30 marks): short, one line each, and they warm you up on the rules the rest of the paper uses. 2. **Section C** (20 marks): read the task statement and the expected output before touching a blank; every blank is checked against that output. 3. **Section D** (10 marks): decide "does it compile" first, then trace only the ones that do. 4. **Section F** last: it cannot lift you above 60, so it should never cost time from the other sections. Syllabus: everything on the slides of Lectures 1 to 11 and everything taught in class. The classroom transcript is beside every slide, in reader mode, under **Transcript**.