要求编写程序计算某年某月某日是该年中的第几天。 这个哪儿有问题求解

#include<stdio.h>
int main()
{
    int year,month,day,i,outday=0;
    scanf("%d/%d/%d",&year,&month,&day);
    for (i=1;i<=month;i++)
        {
            if((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)//闰年
            {
                switch (i)
                {
                    case 4:
                    case 6:
                    case 9:
                    case 11:
                        month=30;
                        break;
                    case 2:
                        month=29;
                        break;
                    default:
                        month=31;
                        break;
                }
            outday+=month;
             } 
             else if (year%400!=0)//平年
             {
                   switch (i)
                {
                    case 4:
                    case 6:
                    case 9:
                    case 11:
                        month=30;
                        break;
                    case 2:
                        month=28;
                        break;
                    default:
                        month=31;
                        break;
                }
            outday+=month; 
            } 
        }
    printf("%d",outday);
    return 0;
 }