Man kan bruge følgende, det er testet med gcc på windows:
Det kan udregne alderen med 100 nano sekunders nøjagtighed, det forudsætter dog at du er født efter 1/1 1601.
#include <iostream>
#include <windows.h>
int main()
{
SYSTEMTIME Now;
GetLocalTime(&Now);
SYSTEMTIME Born;
memset(&Born, 0, sizeof(Born));
std::cout << "Foedt i aar: ";
std::cin >> Born.wYear;
std::cout << "Foedt i maaned: ";
std::cin >> Born.wMonth;
std::cout << "Foedt dag: ";
std::cin >> Born.wDay;
FILETIME NowTime;
SystemTimeToFileTime(&Now, &NowTime);
FILETIME BornTime;
SystemTimeToFileTime(&Born, &BornTime);
unsigned long long N = (NowTime.dwHighDateTime*1ULL << 32) + NowTime.dwLowDateTime;
unsigned long long F = (BornTime.dwHighDateTime*1ULL << 32) + BornTime.dwLowDateTime;
unsigned long long Age = (N - F)/(10ULL*1000*1000);
std::cout << "Age: " << Age << " Seconds" << std::endl;
std::cout << Age/(60*60*24) << " Days" << std::endl;
}