我按照日期计算器的形式写的不知道对不对,请求大家帮我看下对不对?我自己没发现问题

#include <stdio.h>
int main()
{
    int year = 2008;
    int month = 8;
    int day = 8;
    int sum;
    switch(year%400==0||(year%4==0&&year%100!=0))
    {
        case 1:
            if(month%2==0)
            {
                sum = ((month-1)-1)/2*31 + (((month-1)-1)/2-1)*30 + 31 + 29 + day;
            }else
            {
                sum = (month-1)/2*31 + ((month-1)-1)/2*30 + 29 + day;
            }
            break;
        case 0:
            if(month%2==0)
            {
                sum = ((month-1)-1)/2*31 + (((month-1)-1)/2-1)*30 + 31 + 28 + day;
            }else
            {
                sum = (month-1)/2*31 + ((month-1)-1)/2*30 + 28 + day;
            }
            break;
    }
    printf("%d年%d月%d日是该年的第%d天",year,month,day,sum);