Self-Assessment Quiz: Arrays

Twenty questions to confirm the chapter stuck before you move on to procedures. Aim for 16 or more. Answers and a topic map are at the end — do the whole quiz first, and for the "what does this print?" items, work them out by hand before checking.

Question 1

What is the rank of an array declared real(dp) :: a(3, 4, 5)? - A. 3 - B. 12 - C. 60 - D. 5

Question 2

For a default array real(dp) :: v(10), the first element is: - A. v(0) - B. v(1) - C. v(-1) - D. v(10)

Question 3

What does size(a) return for integer :: a(3, 4)? - A. 3 - B. 4 - C. 7 - D. 12

Question 4

The section a(:, 2) of a rank-2 array selects: - A. Row 2 - B. Column 2 - C. The element a(2,2) - D. The first two columns

Question 5

The section v(1:10:2) selects the elements at indices: - A. 1, 2, 3, …, 10 - B. 1, 3, 5, 7, 9 - C. 2, 4, 6, 8, 10 - D. 1 and 10 only

Question 6

For two conformable arrays a and b, the expression a * b computes: - A. The matrix product - B. The dot product - C. The elementwise product a(i)*b(i) - D. A compile error

Question 7

Which computes the true matrix product of two rank-2 arrays? - A. a * b - B. matmul(a, b) - C. dot_product(a, b) - D. product(a, b)

Question 8

True or false, with justification: an array constructor like [1, 2, 3, 4] can be turned into a 2×2 array.

Question 9

What is dot_product([1, 1, 1], [2, 3, 4])? - A. 24 - B. 9 - C. [2, 3, 4] - D. 3

Question 10

For real(dp), allocatable :: a(:) that has been declared but not yet allocated, allocated(a) returns: - A. .true. - B. .false. - C. 0 - D. It is a run-time error to ask

Question 11

When a local allocatable array goes out of scope at the end of a procedure, it is: - A. Leaked until the program ends - B. Automatically deallocated by the language - C. Left dangling and unsafe to use - D. Converted to a pointer

Question 12

Fortran stores a multidimensional array in memory in: - A. Row-major order (last index fastest) - B. Column-major order (first index fastest) - C. Whatever order the compiler picks - D. Random order

Question 13

To sweep a large a(n, n) fast, the inner loop should run over: - A. The second index (columns) - B. The first index (rows) - C. Either — it makes no difference - D. Neither; use a where instead

Question 14

True or false: NumPy's default array order matches Fortran's, so no conversion is ever needed when sharing arrays.

Question 15

What does print *, sum([2, 4, 6]) print (ignoring the leading blank)? - A. 6 - B. 12 - C. [2, 4, 6] - D. 48

Question 16

After integer :: m(2,2); m = reshape([1, 2, 3, 4], [2,2]) (no order argument), what is m(1, 2)? - A. 2 - B. 3 - C. 4 - D. 1

Question 17

The construct where (x < 0.0_dp) x = 0.0_dp does what? - A. Stops the program if any element is negative - B. Sets every element that is currently negative to zero, leaving the rest alone - C. Sets the whole array to zero - D. Returns the count of negative elements

Question 18

count(v > 5) returns: - A. The largest element greater than 5 - B. The number of elements greater than 5 - C. .true. if any element exceeds 5 - D. The positions of elements greater than 5

Question 19

transpose(A) for A = [[1, 2], [3, 4]] (row by row) is: - A. [[1, 2], [3, 4]] - B. [[4, 3], [2, 1]] - C. [[1, 3], [2, 4]] - D. [[2, 4], [1, 3]]

Question 20

What is maxloc([3, 9, 2, 9], dim=1)? - A. 9 - B. 2 - C. 4 - D. [2, 4]

Answer Key

Q Ans Why
1 A Rank is the number of dimensions; a(3,4,5) has three. (Its size is 60.)
2 B Default arrays are one-based; the first element is v(1).
3 D size is the total element count: $3 \times 4 = 12$.
4 B A colon takes the whole extent; a(:, 2) is all rows of column 2.
5 B Triplet 1:10:2 is start 1, stop 10, stride 2 → 1, 3, 5, 7, 9.
6 C * on arrays is elementwise, never a matrix or dot product.
7 B matmul is the matrix product; * is elementwise.
8 True reshape([1,2,3,4], [2,2]) builds a 2×2 array (fills column-major).
9 B $1\cdot2 + 1\cdot3 + 1\cdot4 = 9$.
10 B Declaration reserves the name/rank only; allocated is false until allocate.
11 B Local allocatables auto-deallocate on scope exit — no leak.
12 B Column-major: the first index varies fastest through memory.
13 B Inner loop over the first index walks adjacent memory (cache-friendly).
14 False NumPy defaults to row-major (C order); sharing needs order='F'.
15 B sum([2,4,6]) is 12.
16 B Column-major fill: (1,1)=1, (2,1)=2, (1,2)=3, (2,2)=4 → m(1,2)=3.
17 B where applies the assignment only where the mask is true.
18 B count tallies how many elements satisfy the mask (an integer).
19 C Transpose swaps rows and columns: [[1,3],[2,4]].
20 B maxloc returns the position of the first maximum; 9 first appears at index 2.

Topics to review by question

  • Q1–3 → §5.1–5.2 (rank, shape, size, declaration, 1-based indexing).
  • Q4–5 → §5.2 (array sections and subscript triplets).
  • Q6–7, 9, 19 → §5.3–5.4 (elementwise vs matmul/dot_product/transpose).
  • Q8, 16 → §5.3–5.4 (constructors and reshape — and column-major fill order).
  • Q10–11 → §5.5 (allocatable arrays and automatic deallocation).
  • Q12–14 → §5.6 (column-major layout and loop order).
  • Q15, 18, 20 → §5.4 (reductions and locations).
  • Q17 → §5.7 (where and masks).

Scored below 16? The likeliest gaps are the elementwise-vs-matmul distinction (Q6–7) and column-major order (Q12–13, Q16) — reread §5.4 and §5.6, because both echo through every performance chapter later.