カレンダー

#include <stdio.h>

int main(void)
{
    int year,month,yearm1,monthm1,sum,dayofweek,leapyear,leapyeartotal,days,i;
    int zen_matsu[] = {0,3,3,6,1,4,6,2,5,0,3,5};
    int day[] = {31,28,31,30,31,30,31,31,30,31,30,31};
    char week[][7]  = {"日","月","火","水","木","金","土"};
    printf("カレンダーを出す年を入れてください。>");
    scanf("%d",&year);
    printf("カレンダーを出す月を入れてください。>");
    scanf("%d",&month);
    yearm1 = year - 1;
    monthm1 = month - 1;
    leapyear = ((year % 400 == 0) || (year % 4 == 0 && year % 100 != 0)) ? 1 : 0;
    leapyeartotal = yearm1 / 400 - yearm1 / 100 + yearm1 / 4;
    sum = yearm1 + zen_matsu[monthm1] +
        + leapyear
        + leapyeartotal + 1;
    dayofweek = sum % 7;
    days = ((month != 2) || !leapyear) ? day[monthm1] : day[monthm1] + 1;

    /*
    printf("%d年%d月はうるう年%s、1日が%s曜日で%d日あります。それでカレンダーを作ってください。\n"
        ,year,month,leapyear ? "で":"ではなく" ,week[dayofweek],days);
    */

    printf("      %d 年 %d 月 \n", year, month);

    for(i=0;i<7;i++) printf(" %s",week[i]);
    printf("\n");

    for(i=0;i<21;i++) printf("-");
    printf("\n");

    for(i=0;i<dayofweek;i++) printf("   ");
    for(i=1;i<=days;i++) {
        printf("%3d",i);
        if((dayofweek + i - 1) % 7 == 6) printf("\n");
    }

    return 0;
}