Modern C++ Features

std::map<std::string, std::vector<int>> marks;

// पुराना
std::map<std::string, std::vector<int>>::iterator it = marks.begin();
// modern
auto it2 = marks.begin();

std::vector<int> v = {78, 91, 66};
// पुराना
for (size_t i = 0; i < v.size(); i++) std::cout << v[i] << " ";
// modern
for (int m : v) std::cout << m << " ";          // copy
for (int& m : v) m += 5;                        // वहीं बदलो
for (const auto& m : v) std::cout << m << " ";  // बड़े objects बिना copy पढ़ो

int* p = nullptr;      // modern: अपने type वाली असली null-pointer value
// int* q = NULL;      // पुराना: असल में सिर्फ 0, overload चुनने में उलझन

int count{};                          // 0
std::vector<int> v{1, 2, 3};
struct Point { int x, y; };
Point p{3, 4};
int narrow{3.7};                      // error: braces narrowing conversion रोकते हैं

#include <memory>
// पुराना
Student* s = new Student("Aman");
delete s;                             // भूलना आसान
// modern
auto s2 = std::make_unique<Student>("Aman");   // अपने-आप delete
auto s3 = std::make_shared<Student>("Priya");  // साझा ownership, reference counted

std::sort(v.begin(), v.end(), [](int a, int b) { return a > b; });

#include <iostream>
#include <vector>
#include <utility>

int main() {
    std::vector<int> a(1000000, 7);
    std::vector<int> b = std::move(a);   // कोई element copy नहीं; a खाली रह जाता है
    std::cout << "a: " << a.size() << ", b: " << b.size() << "\n";
    return 0;
}

constexpr int factorial(int n) { return n <= 1 ? 1 : n * factorial(n - 1); }
constexpr int f5 = factorial(5);      // 120, compiler ने निकाला
int table[factorial(4)];              // 24 ints का array

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

std::optional<int> findMarks(const std::map<std::string, int>& m, const std::string& name) {
    auto it = m.find(name);
    if (it == m.end()) return std::nullopt;    // "कोई value नहीं"
    return it->second;
}

int main() {
    std::map<std::string, int> marks{{"Aman", 78}, {"Priya", 91}};

    for (const auto& [name, score] : marks)             // structured bindings
        std::cout << name << " = " << score << "\n";

    if (auto r = findMarks(marks, "Ravi"); r.has_value())   // initialiser वाला if
        std::cout << "Ravi = " << *r << "\n";
    else
        std::cout << "Ravi not found\n";

    std::cout << "Priya = " << findMarks(marks, "Priya").value_or(0) << "\n";
    return 0;
}