输入年月日,输出这是一年中的第几天

#include<stdio.h>
int main()
{
    int year,month,day,leap,sum=0;
    printf("输入年月日：\n");
    scanf("%d%d%d",&year,&month,&day);
        switch(month)
    {
        case 1:sum=0;break;
        case 2:sum=31;break;
        case 3:sum=59;break;
        case 4:sum=90;break;
        case 5:sum=120;break;
        case 6:sum=151;break;
        case 7:sum=181;break;
        case 8:sum=212;break;
        case 9:sum=243;break;
        case 10:sum=273;break;
        case 11:sum=304;break;
        case 12:sum=334;break;
    }
    sum=sum+day;
    if(year%400==0||(year%4==0&&year%100!=0))
        leap=1;
    else leap=0;
    if(leap==1&&month>2)
        sum=sum+1;
    printf("这是%d年的第%d天\n",year,sum);
    return 0;
}