DS Exercises · DS_part1

Formulas go in comments before the code that implements them; integer vs floating-point choices are graded. Edge cases listed per item are part of the task, not decoration.

PF-DS-01 · Count and Proportion

Level: Beginner · Lectures: L05–L06 · Prerequisites: none Problem: Read integers until EOF. Print n: <count>, then even: <p> where <p> is the proportion of even values, 2 decimals. Formula first: p = (number of even values) / n — division is the only floating step; cast exactly once. Input: any integers. Output: two lines as above; n: 0 and even: 0.00 on empty input. Edge cases: empty input; all odd; negative values (−4 is even!). Sample: 1 2 2 7 8 → n: 5 / even: 0.60 Hints: v % 2 == 0 works for negatives on all course compilers; the count is an int, the cast happens at the division. Avoid duplicating: PF-E-067 (sum/mean) — this one is a proportion, no mean.

PF-DS-02 · Min, Max, Range (sentinel)

Level: Beginner · Lectures: L09–L10 · Prerequisites: DS-01 Problem: Read integers until sentinel -999. Print min, max, range (max − min) on separate lines. Sentinel never enters the data. Formula first: range = max − min; trackers initialize from the FIRST data value, never 0. Edge cases: sentinel first → no data; single value → range 0; all-equal. Sample: 4 17 9 22 -999 → min: 4 / max: 22 / range: 18 Hints: one pass; no arrays needed.

PF-DS-03 · Mean of Whole Marks

Level: Beginner · Lecture: L09 · Prerequisites: DS-01 Problem: Read n, then n integer marks 0..100. Print sum and mean (2 dp). Reject the whole run if any mark is outside 0..100: print bad mark and exit 1. Formula first: mean = (x1 + … + xn) / n with the sum in long long. Edge cases: n = 0 → no data (exit 0); n = 100 marks (capacity check with a fixed array of 1000). Sample: 5 82 91 75 68 88 → sum: 404 / mean: 80.80 Hints: this is the strict sibling of PF-E-067: here validation rejects, there input was trusted.

PF-DS-04 · Count Above the Mean (file)

Level: Foundational · Lectures: L17 · Prerequisites: DS-03 Problem: Read doubles from file temperatures.txt (one per line) until EOF. Compute the mean, then print mean (1 dp) and above: <k> — how many values are STRICTLY greater than the mean. Formula first: two passes: mean = Σx/n, then count xi > mean. Discuss (in a comment): why one pass cannot count-above-the-mean. Edge cases: empty file → no data (exit 0); file absent → exit 2 with a message; a single value counts 0 above itself. Dataset: datasets/temperatures.txt (18 readings, mean 20.8 — six values above it). Sample check with the dataset: mean: 20.8 / above: 6 Hints: array capacity 1000; the count is int, values are double.

PF-DS-05 · Median, Both Parities

Level: Foundational · Lecture: L17 · Prerequisites: DS-02 Problem: Read n then n integers. Print the median (1 dp): middle value for odd n, average of the two middles for even n. Formula first: sort ascending; odd n → x((n+1)/2); even n → (x(n/2) + x(n/2+1)) / 2 (1-based). Implement your own insertion or selection sort from L24 — do not re-derive a new sort here. Edge cases: n = 0 → no data; n = 1; duplicates around the median. Sample: 7 88 92 79 85 91 72 95 → median: 88.0; even case 4 10 20 30 40 → median: 25.0 Hints: the even case can produce .5 — that is why the return is double while the data stays int.

PF-DS-06 · Frequency Table with Invalids (file)

Level: Foundational · Lecture: L18 · Prerequisites: DS-05 Problem: Read integers from file survey_ratings.txt (one per line), values expected 1..5. Print a table rating count relative for ratings 1..5 (relative = count/valid, 2 dp), then invalid: <k>. Out-of-range and non-numeric lines both count as invalid but are reported separately (invalid-range, invalid-token totals after the table). Formula first: f(c) = |{x : x = c}|, rel(c) = f(c)/n_valid; index shift counts[r − 1]. Edge cases: all-invalid file (table of zeros, relative 0.00, no division by zero!); missing file → exit 2. Dataset: datasets/survey_ratings.txt (40 lines: 35 valid, 3 out-of-range, 2 non-numeric). Sample check: rating 4 → count 14, relative 0.40; mode: 4 is NOT required here (that is DS-12's job). Hints: getline + istringstream per line (L29 pattern); guard the division by the valid count.