시간 날짜, 요일 출력 초간단 예제 코드

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
    time_t  ltime;
    struct tm *today;
    int daysofmonth[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    char weekstr[][3] = { "일", "월", "화", "수", "목", "금", "토" };
    int year, month, day, month2, th, rmd, adayofweek, OldSec=0;

    while(1){
        time(<ime);
        today = localtime(<ime);

        year = today->tm_year + 1900;
        month = today->tm_mon + 1;
        day = today->tm_mday;

        if (month<=2) {
            rmd = year-1;
            month2 = month+12;
        }
        else {
            rmd = year;
            month2 = month;
        }
        th = rmd/100;
        rmd %= 100;
        adayofweek = (21*th/4 + 5*rmd/4 + 26*(month2+1)/10 + day-1) % 7;

        if ( OldSec != today->tm_sec )
        {
            system("cls");
            printf("%04d. %02d. %02d. (%s) %02d:%02d:%02d KST
",
                // tm_year는 1900을 더해야 서기 연도가 됨
                today->tm_year + 1900,

                // tm_mon은 1월이 0, 2월이 1... 식으로 되어 있음
                today->tm_mon + 1,
                today->tm_mday,
                weekstr[adayofweek],
                today->tm_hour,
                today->tm_min,
                today->tm_sec);
                OldSec = today->tm_sec;
        }
    }
    return 0;
}