输入年月日，计算这一天是一年的第几天？

#include<stdio.h>
int main()
{
    int a[12]={31,28,31,30,31,30,31,31,30,31,30,31};
    int num;
    int years,months,days,i,j=0,flag = 1;
    scanf("%d-%d-%d",&years,&months,&days);
    
    if(years%4==0&&years%100!=0||years%400==0)
    {
        a[1] = 29;
    }
    for(i=0;i<months-1;i++)
    {
        j+=a[i];
    }
num=j+days;
    printf("%d",num);
}