Introduction: control flow

Before starting the unit, measure your starting point. It is a short self-assessment: it is not graded and its result is stored only in your browser.

1. Question 1From earlier unitsWhat is the negation of the condition 1 <= n && n <= 10?

   n < 1 || n > 10

   n < 1 && n > 10

   n <= 1 || n >= 10

   !(1 <= n) && n <= 10

2. Question 2From earlier unitsWith int d{0}; and int n{5};, what happens when d != 0 && n / d > 2 is evaluated?

   It is false, and the division is not computed.

   It is undefined behavior, because of the division by zero.

   It is true.

   It does not compile.

3. Question 3From earlier unitsDivision by repeated subtraction from lesson 1.1 starts with $q = 0$ and $r = a$, and repeats “while $r \geq b$, subtract $b$ from $r$ and add 1 to $q$”. With $a = 20$ and $b = 5$, how many times is the body of the repetition executed?

   4

   5

   3

   20

4. Question 4From earlier unitsWith a 32-bit int, what does the standard guarantee about the value of 46341 * 46341?

   Nothing: the product, $2\,147\,488\,281$, exceeds the maximum of int, and it is undefined behavior.

   That it equals $2\,147\,488\,281$.

   That it equals the maximum of int.

   That the result is computed in long long.

5. Question 5A program contains the chain of decisions if (score >= 50), which writes “Passed”; else if (score >= 90), which writes “Excellent”; and else, which writes “Failed”. What does it write with score equal to 95?

   “Passed”

   “Excellent”

   “Passed” and “Excellent”.

   I don’t know yet.

6. Question 6Which of the following expressions denotes the sum $1 + 2 + \cdots + n$?

   $\displaystyle\sum_{k=1}^{n} k$

   $\displaystyle\sum_{k=1}^{n} n$

   $\displaystyle\sum_{k=0}^{n-1} k$

   $\displaystyle\sum_{k=1}^{k} n$

7. Question 7With int total{0};, what does std::println("{}", total); write after for (int i{0}; i < 5; ++i) { total += i; }?

   10

   15

   5

   I don’t know yet.

8. Question 8In division by repeated subtraction ($q = 0$, $r = a$; while $r \geq b$, $r$ becomes $r - b$ and $q$ becomes $q + 1$), what relation among the variables holds every time the condition is evaluated?

   $a = b \cdot q + r$

   $r < b$

   $q = a / b$

   I don’t know yet.

9. Question 9A procedure starts from an arbitrary integer $n$ (positive, zero or negative) and repeats “while $n > 0$, subtract 2 from $n$”. Does it terminate for every $n$?

   Yes: if $n \leq 0$ it performs no iteration, and if $n > 0$, $n$ goes down 2 at a time and is positive in every iteration, so it cannot go down forever.

   No: with an odd $n$ it skips zero and goes on forever.

   No: with a negative $n$ it subtracts forever.

   Yes, because $n$ is an integer.

10. Question 10What is the greatest common divisor of 84 and 36?

    12

    6

    4

    252

11. Question 11To decide whether 101 is prime by trying divisors, up to which divisor is it enough to go?

    Up to 10.

    Up to 50.

    Up to 100.

    I don’t know yet.