Print string combination without using recursion

print_string_combination.cpp

void PrintCombination(const std::string& str, const std::vector<size_t>& combination) {
  for (size_t i = 0; i < combination.size(); ++i) {
    std::cout << str[combination[i]];
  }
  std::cout << std::endl;
}

void PrintCombinationFixedLength(const std::string& str, size_t combination_length) {
  std::vector<size_t> combination;
  size_t string_length = str.length();
  /* initialize */
  combination.push_back(0);

  while (!combination.empty()) {
    // Initialize if needed
    while (combination.size() < combination_length) {
      combination.push_back(combination.back() + 1);
    }

    PrintCombination(str, combination);

    // Increase the combination by one
    while (!combination.empty()) {
      ++combination.back();
      if (combination.back() > string_length - 1 - (combination_length - combination.size()))
        combination.pop_back();
      else
        break;
    }
  }
}

void PrintCombination(const std::string& str) {
  for (size_t i = 1; i <= str.length(); ++i) {
    PrintCombinationFixedLength(str, i);
  }
}