Exercises · T06 arrays

Covers: 1-D and 2-D arrays — declaration, traversal, fill/print, accumulate/count-if/find-first/min-max, in-place algorithms, 2-D traversals and aggregation, arrays with functions. Lectures L17–L20. Outcomes PF-9.x, PF-10.x.

13 exercises · ladder 🟢 → 🔴.

PF-E-066 · Array Echo

Difficulty: Beginner · Lecture: L17 · Outcomes: PF-9.1 Prerequisites: E-027 Problem: Read n (1–20) then n integers into an array; print them back space-separated on one line, then in reverse order on a second line. Input: n, then n integers · Output: two lines. Sample: 4 5 6 7 8 → 5 6 7 8 / 8 7 6 5 Hints: two loops over the same array — one forward, one with a decreasing index.

PF-E-067 · Array Sum and Mean

Difficulty: Beginner · Lecture: L17 · Outcomes: PF-9.1, PF-9.3 Prerequisites: E-066 Problem: Read n (1–20) then n integers. Print the sum (int) and mean (2 decimals, correctly non-truncating). Input: n, then n integers · Output: sum + mean. Sample: 3 1 2 4 → sum: 7 / mean: 2.33 Hints: L05's truncation lesson — cast after the sum.

PF-E-068 · Fill with Pattern

Difficulty: Beginner · Lecture: L17 · Outcomes: PF-9.1 Prerequisites: E-067 Problem: Declare an array of 10 ints. Fill it so a[i] = 3*i + 2 using a loop, print it, then re-fill with the first 10 squares and print again. Input: none · Output: two arrays. Sample: first → 2 5 8 11 14 17 20 23 26 29 Hints: the fill loop computes — no input needed.

PF-E-069 · Count Occurrences

Difficulty: Beginner · Lecture: L18 · Outcomes: PF-9.3 Prerequisites: E-067 Problem: Read n (1–20), n integers, and a key. Print how many times the key appears and the positions (0-based) of every occurrence. Input: n, integers, key · Output: count + positions. Sample: 6 4 8 4 1 4 9 key 4 → count: 3 / positions: 0 2 4 Hints: COUNT-IF with an index side-report.

PF-E-070 · Min and Max with Positions

Difficulty: Foundational · Lecture: L18 · Outcomes: PF-9.3 Prerequisites: E-069 Problem: Read n (1–20) then n integers. Print the minimum and maximum values and their first positions. Handle the all-equal array. Input: n, then n integers · Output: four numbers. Sample: 5 7 7 2 9 2 → min: 2 (pos 3) / max: 9 (pos 4) Hints: seed with a[0] (L11's lesson), loop from index 1, update value and index together.

PF-E-071 · Reverse In Place

Difficulty: Foundational · Lecture: L18 · Outcomes: PF-9.3 Prerequisites: E-070 Problem: Read n (1–20) then n integers. Reverse the array in place (two-index swap, no second array) and print before/after. Input: n, then n integers · Output: two lines. Sample: 4 1 2 3 4 → before: 1 2 3 4 / after: 4 3 2 1 Hints: swap a[i] with a[n-1-i] for i < n/2.

PF-E-072 · Remove All Occurrences (compact)

Difficulty: Foundational · Lecture: L18 · Outcomes: PF-9.3 Prerequisites: E-071 Problem: Read n (1–20), n integers, and a key. Build a compacted array with all occurrences of key removed (preserve order); print the new logical size and contents. Input: n, integers, key · Output: size + compacted array. Sample: 6 4 8 4 1 4 9 key 4 → size: 3 / 8 1 9 Hints: write-index walks slower than read-index — the classic two-finger compaction.

PF-E-073 · Merge Two Sorted Arrays

Difficulty: Intermediate · Lecture: L20 · Outcomes: PF-9.3, PF-9.4 Prerequisites: E-072 Problem: Read two sorted arrays (n₁, n₁ values; n₂, n₂ values — each ascending). Merge into one sorted array without re-sorting (two-finger walk). Print the merged result. Input: n₁ + values, n₂ + values (each ascending) · Output: merged line. Sample: 3 1 4 9 + 3 2 4 10 → 1 2 4 4 9 10 Hints: take the smaller head each time; then append the remainder.

PF-E-074 · Rotate Left by K

Difficulty: Intermediate · Lecture: L20 · Outcomes: PF-9.3 Prerequisites: E-073 Problem: Read n (1–20), n integers, and k (0–n−1). Rotate the array left by k positions in place is hard; instead produce the rotated result in a second array and print it. Then state (comment) how in-place could be done with three reversals. Input: n, values, k · Output: rotated array. Sample: 5 1 2 3 4 5 k=2 → 3 4 5 1 2 Hints: b[i] = a[(i + k) % n] — modulo does the wrap.

PF-E-075 · Histogram of Scores

Difficulty: Intermediate · Lecture: L20 · Outcomes: PF-9.3, PF-2.3 Prerequisites: E-070 Problem: Read n (1–100) scores (0–100). Print a star histogram: one row per 10-point band (0–9, 10–19, …, 90–100), labeled, with # repeated per count. Reject out-of-range scores with a re-prompt. Input: n + scores · Output: 10 labeled rows. Sample: with three scores in 80s → 80-89: ### Hints: band index = score/10 (with 100 folded into the last band); an array of 10 counters beats 10 variables.

PF-E-076 · Matrix Addition and Scale

Difficulty: Intermediate · Lecture: L20 · Outcomes: PF-10.1, PF-10.2 Prerequisites: E-075 Problem: Read a 2×3 and a 2×3 matrix of ints. Print A+B, then 3×A (each element tripled), matrices formatted in rows. Input: 6 ints, then 6 ints · Output: two matrices. Sample: A = {{1,2,3},{4,5,6}} → 3×A is 3 6 9 / 12 15 18 Hints: nested loops with const int ROWS{2}; const int COLS{3};.

PF-E-077 · Row and Column Totals (2-D)

Difficulty: Intermediate · Lecture: L20 · Outcomes: PF-10.2 Prerequisites: E-076 Problem: Read a 3×4 matrix. Print row totals (one line), column totals (one line), and the grand total. Then print which row has the largest total. Input: 12 ints · Output: three lines + winning row. Sample: — → rows: 22 15 40 / cols: … / grand: 77 / largest row: 2 Hints: accumulator placement (L20's inherited-accumulator bug) decides correctness.

PF-E-078 · Diagonal Difference (square matrix)

Difficulty: Advanced Introductory · Lecture: L20 · Outcomes: PF-10.2, PF-10.3 Prerequisites: E-077 Problem: Read n (2–8) and an n×n matrix. Compute |main diagonal − anti-diagonal| and print it. Also print whether the matrix is symmetric (a[i][j] == a[j][i] for all pairs). Input: n + n² ints · Output: difference + symmetric verdict. Sample: n=2, {{1,2},{2,1}} → diff: 0 / symmetric: yes Hints: diagonals are single loops; symmetry is a j > i half-matrix check.