运行成功结果错误，求解

#include <stdio.h>
int main()
{
    /* 定义需要计算的日期 */
    int year = 2008;
    int month = 8;
    int day = 8;
    int sum,flag;
    /*
     * 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~
     */
    switch(month)
    {
    case 1:sum=day;break;
    case 2:sum=day+31;break;
    case 3:sum=day+31+28;break;
    case 4:sum=day+31+28+31;break;
    case 5:sum=day+31+28+31+30;break;
    case 6:sum=day+31+28+31+30+31;break;
    case 7:sum=day+31+28+31+30+31+30;break;
    case 8:sum=day+31+28+31+30+31+30+31;break;
    case 9:sum=day+31+28+31+30+31+30+31+31;break;
    case 10:sum=day+31+28+31+30+31+30+31+31+30;break;
    case 11:sum=day+31+28+31+30+31+30+31+31+30+31;break;
    case 12:sum=day+31+28+31+30+31+30+31+31+30+31+30;break;
    default:printf("gg");break;
    }

    if(year%400==0||year%4==0&&year%100!=0)
   flag=1;
   else
   flag=0;
   if(flag=1&&month>2)
    sum++;
    printf("%d年%d月%d日是该年的第%d天,year,month,day，sum");