private:

string negatives;

public:

void operator()(int i) {

if (i < 0)

negatives.append(to_string(i) + ",");

}

operator string() {

if (negatives.length() > 0)

negatives.pop_back();

return negatives;

}

string negatives = for_each(numbers.begin(), numbers.end(), GetNegatives());

if (negatives.size() > 0) {

throw invalid_argument("Negatives not allowed: " + negatives);

}

int number = stoi(number_string);

if (number <= 1000)

numbers.push_back(number);

regex numbers_only("(-?\\d+)+");

vector<int> numbers;

for_each(sregex_token_iterator(input.begin(), input.end(), numbers_only),

sregex_token_iterator(),

[&numbers](string s) { add_if_valid(numbers, s); });

return numbers;

if (input.empty())

return 0;

vector<int> numbers = get_numbers(input);

check_for_negatives(numbers);

return accumulate(numbers.begin(), numbers.end(), 0);

}