exercism/cpp/making-the-grade

Making the Grade

Welcome to Making the Grade on Exercism's C++ Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Arrays and Vectors

C++ offers different containers to store elements of the same type in an ordered way. There is std::array for containers of a fixed size and std::vector, which comes with dynamic resizing capabilities.

Construction

When you declare an array or a vector you need to specify the type of elements, that container will hold. Arrays also need a size. Look at these examples to see the two container types' initializations:

#include <array>
#include <string>

// std::array<element_type, size> variable_name {list of elements}
std::array<std::string, 3> indie_rock {"yeah", "yeah", "yeah"};
// indie_rock contains the elements "yeah" three times

Vectors usually need more space, as they allocate memory for further growth. You do not need to specify a size:

#include <vector>

// std::vector<element_type> variable_name {list of elements}
std::vector<int> countdown {3, 2, 1};
// countdown contains the elements 3, 2 and 1

Note: You do not need to know the exact mechanics behind the template concept yet, it will have its own concept further down the syllabus tree.

Element access

Vectors and arrays share the same functions to access their elements. You can use the member functions front and back to get the first and last elements of the container. There is also at and the [] operator to access specific elements.

countdown[0];
// => 3
countdown.at(2);
// => 1
countdown[1] = 4;
// countdown now contains 3, 4 and 1
indie_rock.back() = "yeahs";
// indie_rock is now "yeah", "yeah", "yeahs"

Note: If you pick a position that is not in the range of your container, [] might lead to undefined behavior. The at function would raise an exception, which might make your life easier in the long term.

Vector modifiers

As a vector is not fixed in size, it is possible to add or remove elements. Two common functions for that purpose are emplace_back and pop_back.

std::vector<std::string> witches {"Holly", "Alyssa", "Shannen"};
witches.pop_back();
// Shannen is no longer with the witches
witches.emplace_back("Rose");
// Rose has joined the team

Capacity

You can check the containers for emptiness with the member function empty. If you want to know the number of elements, you can use size.

Instructions

You're a teaching assistant correcting student exams. Keeping track of results manually is getting both tedious and mistake-prone. You decide to make things a little more interesting by putting together some functions to count and calculate results for the class.

1. Rounding Scores

While you can give "partial credit" on exam questions, overall exam scores have to be ints. So before you can do anything else with the class scores, you need to go through the grades and turn any double scores into ints.

Create the function round_down_scores() that takes a vector of student_scores. The schools' requested rounding is a truncation. Lucky for you, C++ can cast one type into another with static_cast. The static_cast conversion from double to int cuts off any digit after the decimal. This function should take the input vector and return a new vector with all the scores converted to ints.

std::vector<double> student_scores {90.33, 40.5, 55.44, 70.05, 30.55, 25.45, 80.45, 95.3, 38.7, 40.3};
round_down_scores(student_scores)
// => {90, 40, 55, 70, 30, 25, 80, 95, 38, 40}

2. Non-Passing Students

As you were grading the exam, you noticed some students weren't performing as well as you'd hoped. But you were distracted, and forgot to note exactly how many students.

Create the function count_failed_students() that takes a vector of student_scores. This function should count up the number of students who don't have passing scores and return that count as an integer. A student needs a score greater than 40 to achieve a passing grade on the exam.

count_failed_students({90,40,55,70,30,25,80,95,38,40});
// => 5

3. The "Best"

The teacher you're assisting wants to find the group of students who've performed "the best" on this exam. What qualifies as "the best" fluctuates, so you need to find the student scores that are greater than or equal to the current threshold.

Create the function above_threshold() taking student_scores (a vector of grades), and threshold (an int, the "top score" threshold) as parameters. This function should return a vector of all scores that are >= to threshold.

above_threshold({90,40,55,70,30,68,70,75,83,96}, 75);
// => {90,75,83,96}

4. Calculating Letter Grades

The teacher you're assisting likes to assign letter grades as well as numeric scores. Since students rarely score 100 on an exam, the "letter grade" lower thresholds are calculated based on the highest score achieved, and increment evenly between the high score and the failing threshold of <= 40.

Create the function letter_grades() that takes the "highest" score on the exam as a parameter, and returns an array (not a vector) of lower score thresholds for each "American style" grade interval: ["D", "C", "B", "A"].

/*Where the highest score is 100, and failing is <= 40.
       "F" <= 40
 41 <= "D" <= 55
 56 <= "C" <= 70
 71 <= "B" <= 85
 86 <= "A" <= 100
*/

letter_grades(100);
// => {41, 56, 71, 86}


/*Where the highest score is 88, and failing is <= 40.
       "F" <= 40
 41 <= "D" <= 52
 53 <= "C" <= 64
 65 <= "B" <= 76
 77 <= "A" <= 88
*/

letter_grades(88);
// => {41, 53, 65, 77}

5. Matching Names to Scores

You have exam scores in descending order, and the respective student names (sorted in the order of their exam scores). You would like to match each student's name with their exam score and print out an overall class ranking.

Create the function student_ranking() with parameters student_scores and student_names. Match each student name on the student_names vector with their score from the student_scores vector. You can assume each argument vector is sorted from highest score(er) to lowest score(er). The function should return a vector of strings with the format <rank>. <student name>: <student score>.

std::vector<int> student_scores {100, 99, 90, 84, 66, 53, 47};
std::vector<std::string> student_names {"Joci", "Sara","Kora","Jan","Indra","Bern", "Fred"};
student_ranking(student_scores, student_names)
// =>
//  {"1. Joci: 100", "2. Sara: 99", "3. Kora: 90", "4. Jan: 84", "5. Indra: 66", "6. Bern: 53", "7. Fred: 47"}

6. A "Perfect" Score

Although a "perfect" score of 100 is rare on an exam, it is interesting to know if at least one student has achieved it.

Create the function perfect_score() with parameters student_scores and student_names. The lists are the same as in task 5. The function should return the first <name> (as a string) of the student who scored 100 on the exam.

If no 100 scores are found, an empty string "" should be returned.

perfect_score({"Nur", "Tony", "Fatima"}, {90, 80, 100});
// => "Fatima"

perfect_score({"Nur", "Tony"}, {90, 80});
// => ""

Source

Created by

• @vaeng