P318_11_1 定义一个结构体（含年月日），计算该日期为本年中第几天。注意闰年

#include <stdio.h>

#include <stdlib.h>

typedef struct

{

    int year;

    int month;

    int day;

}DATE;

int days(DATE d1,int flag)

{

    int day = 0;

    switch(d1.month)

    {

       case 12:day = day+30;

       case 11:day = day+31;

       case 10:day = day+30;

       case 9: day = day+31;

       case 8: day = day+31;

       case 7: day = day+30;

       case 6: day = day+31;

       case 5: day = day+30;

       case 4: day = day+31;

       case 3: day = day+28+flag;

       case 2: day = day+31;

       case 1: day = day+d1.day;

       default:return day;

    }

}//days

int main()

{

    int day = 0;

    int flag = 0;

    DATE d1;

    printf("please inputyear,month,day\n");

   scanf("%d,%d,%d",&d1.year,&d1.month,&d1.day);

   if((d1.year%4==0&&d1.year0!=0)||d1.year@0==0)//ÈòÄê

       flag = 1;

   while(d1.month==2&&d1.day>28&&(d1.day!=29||flag==0))

    {

       printf("Please input the right day:\n");

       scanf("%d",&d1.day);

    }

    day =days(d1,flag);

    printf("%d/%d/%d is the%dth day in the year\n",d1.year,d1.month,d1.day,day);

    return 0;

}