03. Histogram

#include <iostream>

using namespace std;

int main() {
    double p1 = 0.0, p2 = 0.0, p3 = 0.0, p4 = 0.0, p5 = 0.0;

    int num;
    cin >> num;

    int number;

    for (int i = 0; i < num; i++) {
        cin >> number;

        if (number < 200) {
            p1++;
        }
        else if (number < 400) {
            p2++;
        }
        else if (number < 600) {
            p3++;
        }
        else if (number < 800) {
            p4++;
        }
        else {
            p5++;
        }
    }

    cout.setf(ios::fixed);
    cout.precision(2);

    cout << p1 / num * 100 << "%" << endl;
    cout << p2 / num * 100 << "%" << endl;
    cout << p3 / num * 100 << "%" << endl;
    cout << p4 / num * 100 << "%" << endl;
    cout << p5 / num * 100 << "%" << endl;

    return 0;
}

Решение с речник, тернарен оператор и foreach:

#include <iostream>
#include<string>
#include<map>

using namespace std;

int main() {
    map <string, double> histogram = { {"p1", 0.0}, {"p2", 0.0}, {"p3", 0.0}, {"p4", 0.0}, {"p5", 0.0} };

    int num;
    cin >> num;

    int number;

    for (int i = 0; i < num; i++) {
        cin >> number;

        string p =
            number < 200 ? "p1" :
            number < 400 ? "p2" :
            number < 600 ? "p3" :
            number < 800 ? "p4" : "p5";

        histogram[p]++;
    }

    cout.setf(ios::fixed);
    cout.precision(2);

    for (string i : {"p1", "p2", "p3", "p4", "p5"}) {
        cout << histogram[i] / num * 100 << "%" << endl;
    }

    return 0;
}