C++ Lambda Expression Recursive calls

#include <iostream>
#include <functional>                  // For function<>

int main()/*w  w  w .  j  av  a2s  .  co m*/
{
  std::function<long long(long long, long long)> hcf = [&hcf](long long i, long long j) mutable ->long long   {
                               if (i < j)
                                  return hcf(j, i);
                               long long remainder{i%j};
                               if (!remainder)
                                  return j;
                               return hcf(j, remainder);
   };

  auto showHCF = [&hcf](long long a, long long b) {
       std::cout << "The highest common factor of " << a << " and " << b << " is " << hcf(a, b) << std::endl;
  };

  long long a {}, b {};

  while (true) {
    std::cout << "\nEnter two integers to find their HCF, or 0 to end: ";
    std::cin >> a;
    if (!a) break;
    std::cin >> b;

    showHCF(a, b);
  }
}