我这段程序为什么不行啊，大神帮忙看下，跪谢

int sum;

    switch(month)    /*对月份进行情况讨论

    {

        case 1;sum = 0+day;break;

        case 2;sum = 31+day;break;

        case 3;sum = 31+28+day;break;

        case 4;sum = 31+28+31+day;break;

        case 5;sum = 31+28+31+30+day;break;

        case 6;sum = 31+28+31+30+31+day;break;

        case 7;sum = 31+28+31+30+31+30+day;break;

        case 8;sum = 31+28+31+30+31+30+31+day;break;

        case 9;sum = 31+28+31+30+31+30+31+31+day;break;

        case 10;sum = 31+28+31+30+31+30+31+31+30+day;break;

        case 11;sum = 31+28+31+30+31+30+31+31+30+31+day;break;

        case 12;sum = 31+28+31+30+31+30+31+31+30+31+30+day;break;

        default:printf("一年当中只有12个月哦");break;

    }

    sum = sum+day;

    if(year%4 == 0)

    {

       if(month < 3)

         {

         printf("%d年%d月%d日是该年的第%d天",year,month,day,sum);

         }

       printf("%d年%d月%d日是该年的第%d天",year,month,day,sum+1);

    }

    else

    {

    printf(%d年%d月%d日是该年的第%d天",year,month,day,sum)；

    }