练习-用switch语句实现输入某年某月某日，判断这一天是这一年的第几天

可以参考以下代码实现：

#include <stdio.h>

int main() {
    int year, month, day, sum = 0;
    printf("请输入年月日，格式为yyyy-mm-dd：");
    scanf("%d-%d-%d", &year, &month, &day);
    switch (month) {
        case 12: sum += 30;
        case 11: sum += 31;
        case 10: sum += 30;
        case 9: sum += 31;
        case 8: sum += 31;
        case 7: sum += 30;
        case 6: sum += 31;
        case 5: sum += 30;
        case 4: sum += 31;
        case 3:
            if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                sum += 29;
            } else {
                sum += 28;
            }
        case 2: sum += 31;
        case 1: sum += day;
    }
    printf("%d年%d月%d日是这一年的第%d天\n", year, month, day, sum);
    return 0;
}