程序代码：

#include"stdio.h"
#include"math.h"
void main()
{
    unsigned year,month,day,sum,leap;
    printf("请输入年,月,日：\n");
    scanf("%u,%u,%u",year,month,day);
    switch(month)
    {
        case 1:
            sum=0;
            break;
        case 2:
            sum=31;
            break;
        case 3:
            sum=31+28;
            break;
        case 4:
            sum=31+28+31;
            break;
        case 5:
            sum=31+28+31+30;
            break;
        case 6:
            sum=31+28+31+30+31;
            break;
        case 7:
            sum=31+28+31+30+31+30;
            break;
        case 8:
            sum=31+28+31+30+31+30+31;
            break;
        case 9:
            sum=31+28+31+30+31+30+31+31;
            break;
        case 10:
            sum=31+28+31+30+31+30+31+31+30;
            break;
        case 11:
            sum=31+28+31+30+31+30+31+31+30+31;
            break;
        case 12:
            sum=31+28+31+30+31+30+31+31+30+31+30;
            break;
        default:
            printf("Dataerror\n");
    }
    sum=sum+day;
    if(year%4==0)
    {
        leap=1;
    }
    else
    {
        leap=0;
    }
    if(leap==1&&month>2)
    {
        ++sum;
    }

    printf("第%u天\n",sum);


}