[C]计算某一天是该年中的第几天

输入年月份，计算今天是今年的第几天？

#include<stdio.h> 
void main() 
{ 
    int year,month,day,days,i,d; 
    printf("请输入年，月，日：\n"); 
    scanf("%d,%d,%d",&year,&month,&day); 
    days=0; 
    for(i=1;i<month;i++) 
    { 
        switch(i) 
        { 
            case 1: 
            case 3: 
            case 5: 
            case 7: 
            case 8: 
            case 10: 
            case 12:d=31;break; 
            case 4: 
            case 6: 
            case 9: 
            case 11:d=30;break; 
            case 2:if(year%4==0&&year%100!=0||year%400==0) 
                       d=29; 
                   else d=28; 
        } 
        days+=d; 
    } 
    printf("%d年%d月%d日是这一年的第%d天。\n",year,month,day,days+day); 
}