#include <iostream>
#include <functional>

std::function<double(double, double)> ops[] = {[](double x, double y){return x+y;}, [](double x, double y){return x-y;}, [](double x, double y){return x*y;}, [](double x, double y){return x/y;}};

int main()
{
    int act=-1;
    double v1, v2;
    std::cout << "Hello. How much you smoked marijuana that the calculator talking to you?" << std::endl << "Actions:\n1 - addition\n2 - subtraction\n3 - multiplication\n4 - division\n0 - exit" << std::endl;
    do
    {
        std::cout << "Enter action: " << std::endl;
        std::cin >> act;
    } while (act < 0 || act > 4);

    return (act == 0) ? 0 : (std::cout << "and now for some values: ", std::cin >> v1 >> v2, std::cout << ops[act - 1](v1, v2) << std::endl, 0);
}