c++ 1 1 placeholder

#include <iostream>     // std::cout, std::boolalpha
#include <functional>   // std::bind, std::plus, std::placeholders, std::is_bind_expression

int main() {
    using namespace std::placeholders;  // introduces _1
    auto increase_int = std::bind(std::plus<int>(), _2, 1);

    std::cout << std::boolalpha;
    std::cout << std::is_bind_expression<decltype(increase_int)>::value << '\n';

    return 0;
}

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

using namespace std;

int main()
{
    int numbers[] = { 10,20,30,40,50,10 };
    int cx;
    cx = count_if(numbers, numbers + 6, bind(less<int>(), std::placeholders::_1, 100));
    cout << "There are " << cx << " elements that are less than 40.\n";

    cx = count_if(numbers, numbers + 6, bind(less<int>(),100, std::placeholders::_2));
    cout << "There are " << cx << " elements that are not less than 40.\n";

    system("pause");
    return 0;
}

#include <iostream>
#include <thread>
int main()
{
    unsigned int in = std::thread::hardware_concurrency();
    std::cout << in << std::endl;
}

#include <iostream>
#include<list>
using namespace std;
int main()
{
    std::cout << "Hello World!\n";
    list<int >  li{ 1,2,3,4 };
    list<int>::iterator it1;
    //list<int>::iterator it2;
    it1 = li.begin();
//it2 = it1;
    while (true) {
        list<int>::iterator it2=it1;

        it2++;
        cout <<"\n" ;
        if (it2 == li.end())
        {
           // cout << *it2;
            cout << "hello";
            break;
        }
        if(it1!=li.end())
        {
            it1++;
            cout << "\n";
        }
        if(it1==li.end())
        {
            it1--;
        }
    }
  //  cout << *it2;
}