int CDate::operator-(const CDate d)const{
int days;
int nm = (_Month + 9) % 12; //
int ny = _Year - nm / 10;
int nd = 365 * ny + ny / 4 - ny / 100 + ny / 400 + (nm * 306 + 5) / 10 + (_Day - 1);
int nm1 = (d._Month + 9) % 12;
int ny1 = d._Year - nm1 / 10;
int nd1 = 365 * ny1 + ny1 / 4 - ny1 / 100 + ny1 / 400 + (nm1 * 365 + 5) / 10 + (d._Day - 1);
days = nd - nd1;
return days;
}