#include <iostream>     
#include <string>

int main () {
  int m{5}, n{6};

  auto f1 = [](int x)->int{return x + 1;};   // a function that returns x + 1. 
  auto f2 = [m](int x){return x + m;};       // can read m from local context.
  auto f3 = [=](int x){return x + m + n;};   // can read all local variables from local context.
  auto f4 = [&m](){++m;};                    // access to m by reference - can write.
  auto f5 = [&](){++m; n--;};                // access to all variables in local context by ref.
  auto f6 = [&]{++m;};                       // the empty parameter list is implicit.

  std::cout << f1(1) << std::endl;     // 2
  std::cout << f2(1) << std::endl;     // 6
  std::cout << f3(1) << std::endl;     // 12

  f4();                                // m becomes 6
  f5();                                // m becomes 7, n becomes 5
  f6();                                // m becomes 8
  
  std::cout << "m: " << m << " n: " << n << std::endl;    // m: 8 n: 5

}