C++ · STL: algorithms

STL algorithms take an iterator range [first, last), so one std::sort works for vectors, arrays and deques alike. Most loops I’d write by hand already have a name:

loop that…	algorithm
sorts	std::sort(b, e, cmp)
finds the first match	std::find_if
counts matches	std::count_if
sums or folds	std::accumulate (<numeric>)
maps each element	std::transform
finds the min/max	std::min_element, std::max_element, std::minmax_element

#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <vector>

struct Rec { std::string name; int marks; };

int main() {
    std::vector<Rec> rs{{"Asha", 72}, {"Sahaj", 88}, {"Ravi", 35}, {"Meet", 91}};

    std::sort(rs.begin(), rs.end(), [](const Rec& a, const Rec& b) { return a.marks > b.marks; });
    for (auto& r : rs) std::cout << r.name << ':' << r.marks << ' ';
    std::cout << '\n';

    auto failed = std::find_if(rs.begin(), rs.end(), [](const Rec& r) { return r.marks < 40; });
    std::cout << "first fail: " << failed->name << '\n';

    int passed = std::count_if(rs.begin(), rs.end(), [](const Rec& r) { return r.marks >= 40; });
    int total = std::accumulate(rs.begin(), rs.end(), 0, [](int s, const Rec& r) { return s + r.marks; });
    std::cout << "passed " << passed << ", mean " << static_cast<double>(total) / rs.size() << '\n';

    std::vector<int> v{4, 1, 7, 3};
    std::vector<int> sq(v.size());
    std::transform(v.begin(), v.end(), sq.begin(), [](int x) { return x * x; });
    auto [mn, mx] = std::minmax_element(sq.begin(), sq.end());
    std::cout << "squares min " << *mn << " max " << *mx << '\n';
}

Output:

Meet:91 Sahaj:88 Asha:72 Ravi:35 
first fail: Ravi
passed 3, mean 71.5
squares min 1 max 49