c++计算改日是本年的第几天

任务描述：

定义一个结构体变量（包括年、月、日），编写程序，要求输入年、月、日，程序能计算并输出该日在本年中是第几天。注意闰年问题。

测试输入：

2000 12 20

预期输出：

12/20 is the 355th day in 2000

程序源码：

#include <iostream>
using namespace std;
struct
{ 
int year;
int month;
int day;
}date;

int main()
{
int days;
cin>>date.year>>date.month>>date.day;

// 请在此添加代码
    /********** Begin *********/
    days=0;    
    switch(date.month)
    {
        case 12: days=days+30;
        case 11: days=days+31;
        case 10: days=days+30;
        case 9: days=days+31;
        case 8: days=days+31;
        case 7: days=days+30;
        case 6: days=days+31;
        case 5: days=days+30;
        case 4: days=days+31;
        case 3: if(date.year%4==0 && date.year%100!=0 ||date.year%400==0)
                    days=days+29;
                else days=days+28;
        case 2: days=days+31;
        case 1: days=days+date.day;
        default :break;
    }
    
    
    /********** End **********/

cout<<date.month<<"/"<<date.day<<" is the "<<days<<"th day in "<<date.year<<"."<<endl;
return 0;
}