DateToDay

date2day.cpp

const int days[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
int days_acc[13] = {0};

partial_sum(days, days+12, days_acc+1);

int date2day(int m, int d)
{
    return days_acc[m] + d;
}