为什么运行成功,输出错误 2008年8月8日这一天，是该年中的第809337664天

#include <stdio.h>
int main()
{
    /* 定义需要计算的日期 */
    int year = 2008;
    int month = 8;
    int day = 8;
    /*
     * 请使用switch语句，if...else语句完成本题
     * 如有想看小编思路的，可以点击左侧任务中的“不会了怎么办”
     * 小编还是希望大家独立完成哦~
     */
    int sum,feb;
    if(year%4==0&&year%100!=0||year%400==0)
    {
        feb=29;
    }   
    else
    {
        feb=28;
    }   
    int jan,mar,may,jul,aug,oct=31;
    int apr,jun,sep,nov=30;
    switch(month)
    {
        case 1:
        sum=day;
        break;
        case 2:
        sum=day+jan;
        break;
        case 3:
        sum=day+jan+feb;
        break;
        case 4:
        sum=day+jan+feb+mar;
        break;
        case 5:
        sum=day+jan+feb+mar+apr;
        break;
        case 6:
        sum=day+jan+feb+mar+apr+may;
        break;
        case 7:
        sum=day+jan+feb+mar+apr+may+jun;
        break;
        case 8:
        sum=day+jan+feb+mar+apr+may+jun+jul;
        break;
        case 9:
        sum=day+jan+feb+mar+apr+may+jun+jul+aug;
        break;
        case 10:
        sum=day+jan+feb+mar+apr+may+jun+jul+aug+sep;
        break;
        case 11:
        sum=day+jan+feb+mar+apr+may+jun+jul+aug+sep+oct;
        break;
        case 12:
        sum=day+jan+feb+mar+apr+may+jun+jul+aug+sep+oct+nov;
        break;
        default:printf("一年当中只有12个月哦~");
        break;
    }
    printf("%d年%d月%d日这一天，是该年中的第%d天",year,month,day,sum);
 return 0;
}