http://ustc.openjudge.cn/ex2/3/

calendar.c

#include<stdio.h>
struct cal {
    int hour, minute, second, day, month, year;
};

struct cal convert(struct cal in) {
    struct cal out;
    in.year -= 2000;
    int past_years = in.month >= 3 ? in.year + 1 : in.year;
    int days = in.year * 365 + (past_years + 3) / 4 - (past_years + 99) / 100 + (past_years + 399) / 400;
    const int month[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    int i;
    for (i=0; i < in.month - 1; i++)
        days += month[i];
    days += in.day - 1;

    out.day = days % 100 + 1;
    days /= 100;
    out.month = days % 10 + 1;
    days /= 10;
    out.year = days;

    unsigned int time = (long long)(in.hour * 3600 + in.minute * 60 + in.second) * 100000 / 86400;
    out.second = time % 100;
    time /= 100;
    out.minute = time % 100;
    time /= 100;
    out.hour = time;
    return out;
}

int main() {
    int i, n;
    scanf("%d", &n);
    for (i=0; i<n; i++) {
        struct cal c, out;
        scanf("%d:%d:%d %d.%d.%d", &c.hour, &c.minute, &c.second, &c.day, &c.month, &c.year);
        out = convert(c);
        printf("%d:%d:%d %d.%d.%d\n", out.hour, out.minute, out.second, out.day, out.month, out.year);
    }
    return 0;
}