#include #include #include #include //for istream_iterator #include //for copy_n using namespace std; long int sum(long int n); int main() { errno = 0; cout << "Content-type: text/html\n" "\n" "\n" "\n" "\n" "Summation\n" "\n" "\n" "\n" "

Summation

\n" "

\n"; const char *const p {getenv("CONTENT_LENGTH")}; if (p == nullptr) { cout << "environment has no CONTENT_LENGTH

\n"; return EXIT_FAILURE; } const int length {atoi(p)}; string s; copy_n(istream_iterator(cin), length, back_insert_iterator(s)); long int n {0}; try { //n is the number that the user input n = stol(s.substr(2), nullptr, 10); } catch (const invalid_argument &ex) { cout << "Sorry, \"" << s.substr(2) << "\" is not a valid number.

\n"; return EXIT_FAILURE; } catch (const out_of_range &ex) { cout << "Sorry, \"" << s.substr(2) << "\" is out of range.

\n"; return EXIT_FAILURE; } cout << "The sum of the integers from 1 to " << n << " is \n" << "
\n" << sum(n) << "\n" << "

\n" << "\n" << "\n"; return EXIT_SUCCESS; } //Return the sum of the integers from 1 to n inclusive. long int sum(long int n) { return n * (n + 1) / 2; }