function_pointers.cpp

#include <iostream>
#include <vector>
#include <functional>
#include <algorithm>

using namespace std;

// 1. Обычные функции
int add(int a, int b) { return a + b; }
int subtract(int a, int b) { return a - b; }
int multiply(int a, int b) { return a * b; }

// 2. Callback
int calculate(int a, int b, int (*operation)(int, int)) {
    return operation(a, b);
}

// 3. std::function
int calculateFunc(int a, int b, function<int(int, int)> operation) {
    return operation(a, b);
}

int main() {
    cout << "=== Урок 21: Указатели на функции ===\n\n";

    // 1. Указатель на функцию
    cout << "1. Указатель на функцию\n";
    int (*funcPtr)(int, int);

    funcPtr = add;
    cout << "funcPtr(5, 3) = " << funcPtr(5, 3) << " (add)\n";

    funcPtr = subtract;
    cout << "funcPtr(5, 3) = " << funcPtr(5, 3) << " (subtract)\n";

    funcPtr = multiply;
    cout << "funcPtr(5, 3) = " << funcPtr(5, 3) << " (multiply)\n\n";

    // 2. Callback
    cout << "2. Callback\n";
    cout << "calculate(10, 5, add) = " << calculate(10, 5, add) << endl;
    cout << "calculate(10, 5, subtract) = " << calculate(10, 5, subtract) << "\n\n";

    // 3. std::function
    cout << "3. std::function\n";
    function<int(int, int)> op = add;
    cout << "op(10, 5) = " << op(10, 5) << endl;
    op = multiply;
    cout << "op(10, 5) = " << op(10, 5) << " (после op = multiply)\n\n";

    // 4. Лямбда
    cout << "4. Лямбда-функции\n";
    auto square = [](int x) { return x * x; };
    cout << "square(5) = " << square(5) << endl;

    cout << "Лямбда как callback: "
         << calculateFunc(10, 5, [](int a, int b) { return a * b; }) << "\n\n";

    // 5. Лямбды в STL
    cout << "5. Лямбды в sort\n";
    vector<int> nums = {5, 2, 8, 1, 9};
    cout << "До: ";
    for (int x : nums) cout << x << " ";
    cout << endl;

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

    cout << "После сортировки (убывание): ";
    for (int x : nums) cout << x << " ";
    cout << "\n\n";

    // 6. Калькулятор
    cout << "6. Калькулятор\n";
    int a = 12, b = 4;
    cout << a << " + " << b << " = " << calculate(a, b, add) << endl;
    cout << a << " - " << b << " = " << calculate(a, b, subtract) << endl;
    cout << a << " * " << b << " = " << calculate(a, b, multiply) << endl;

    auto divide = [](int x, int y) {
        if (y == 0) return 0;
        return x / y;
    };
    cout << a << " / " << b << " = " << calculateFunc(a, b, divide) << "\n";

    return 0;
}