const Correctness

Lab C++ Intermediate 20 points

Write class Polygon holding points with a const method perimeter(). A free function void report(const Polygon &p) can only call const methods. Read a polygon and report its perimeter (2 decimals) and number of points.

Input

n, then n lines x y.

Output

One line: points=N perimeter=P

Example

Input

Output

points=4 perimeter=14.00

Sample input available Sample output available

Editor

C++

Hints

Methods that don't modify the object should be marked const.

A const reference can only call const methods.

Solution explanation

const correctness lets the compiler enforce "this function won't change that object".

Show solution

#include <iostream>
#include <iomanip>
#include <vector>
#include <cmath>
using namespace std;

class Polygon {
public:
    void add(double x, double y) { pts_.push_back({x, y}); }
    size_t size() const { return pts_.size(); }
    double perimeter() const {
        double total = 0;
        for (size_t i = 0; i < pts_.size(); i++) {
            const auto &a = pts_[i];
            const auto &b = pts_[(i + 1) % pts_.size()];
            total += hypot(a.first - b.first, a.second - b.second);
        }
        return total;
    }

private:
    vector<pair<double, double>> pts_;
};

void report(const Polygon &p) {
    cout << fixed << setprecision(2) << "points=" << p.size() << " perimeter=" << p.perimeter() << "\n";
}

int main() {
    int n;
    cin >> n;
    Polygon p;
    for (int i = 0; i < n; i++) {
        double x, y;
        cin >> x >> y;
        p.add(x, y);
    }
    report(p);
    return 0;
}

Output

Answer