flag咋回事，一下是0，一下是1

#include"stdio.h"
int main()
{
    int year, i, flag=0;
    scanf("%d", &year);
    if(year <= 2000 || year >= 2101)
    {
        printf("Invalid year!");
    }
    else
    {
        for(i = 2001;i <= year;i++)
        {
            if((i%4 == 0 && i%100 != 0) || (i%400 == 0))            
            {
                flag = 1;
                printf("%d\n", i);
              }
        }
        if(flag == 0)
        {
            printf("None");
        }
    }
    return 0;
}