1.環境：

2.程式碼：

/*

 *wuxiuwen
 *input date, the date of this year is calculated which day.
 *輸入一個日期(年月日)，計算是這一年中的第幾天 
 */
#include<stdio.h>

int dm(int year,int month, int day)
{
        int flag=0;
        if((year%4==0 && year%100!=0) || (year%400==100))flag = 1;
        else flag =0;
        int a=0;
        switch(month-1)
        {
                case 11 :a+=30;
                case 10 :a+=31;
                case 9 :a+=30;
                case 8 :a+=31;
                case 7 :a+=31;
                case 6 :a+=30;
                case 5 :a+=31;
                case 4 :a+=30;
                case 3 :a+=31;
                case 2 :a+=28+flag;
                case 1 :a+=31;break;
                default :printf("Please input others\n");
        }
        a +=day;
        printf("THIS IS THE %d DAY OF %d.\n",a,year);
}
int main()
{
        int day,month,year;
        printf("please input the date(year.month.day):\n");
        scanf("%d.%d.%d",&year,&month,&day);
        dm(year,month,day);
        return 0;

}

3.說明：