gmpxx_test.cxx

#include <iostream>
#include <ctime>
#include <gmpxx.h>

typedef mpz_class Integer;

Integer N[] = {1, 12, 123, 1234, 12345, 123456};

Integer sum_digits(Integer n);
Integer factorial(Integer n);

int main(int argc, char *argv[])
{
	Integer res = 0;
	std::clock_t start = std::clock();
	for(int i = 0; i < sizeof(N)/sizeof(Integer); ++i)
	{
		res += sum_digits(factorial(N[i]));
	}
	std::cout << res << std::endl;
	std::clock_t end = std::clock();
	std::cout << "Execution time: "
		<< 1e3 * ((double) (end - start)) / CLOCKS_PER_SEC 
		<< " ms" << std::endl;
}

Integer factorial(Integer n)
{
	Integer res = 1;
	for(Integer k = n; k > 1; k -= 1)
		res *= k;
	return res;
}

Integer sum_digits(Integer n)
{
	Integer res = 0;
	std::string s = n.get_str();
	for(auto i = s.begin(); i != s.end(); ++i)
		res += (int) *i - (int) '0';
	return res;
}