我试了试，这两个都行

怎么可能啊，测试过平年的结果对吗？

#include <stdio.h>

int main()
{
    int dayofmonth[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    
    int day,month,year;
    printf("Input year,month,day:");
    scanf("%d,%d,%d",&year,&month,&day);
    
    int i,total=day;
    
    for(i=1;i<month;i++)
    {
        total+=dayofmonth[i];
    }
    
    if(year%400==0||(year%4==0&&year%100!=0))
    {
        if(month>2)  total+=1;
    }
    
    printf("It is the %dth day of the year\n",total);
    
    return 0;
}

[此贴子已经被作者于2016-3-25 15:22编辑过]

这样改一下更好

#include <stdio.h>

int main()
{
    int dayofmonth[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };

    int day, month, year;
    printf("Input year,month,day:");
    scanf("%d,%d,%d", &year, &month, &day);

    int i, total = day;

    if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))
    {
        dayofmonth[2] += 1;
    }

    for (i = 1; i<month; i++)
    {
        total += dayofmonth[i];
    }
    printf("It is the %dth day of the year\n", total);

    return 0;
}

哦   ok，ok，

哇，真棒，还可以这样

好多写法呀

int dayofmonth[]={0,0,31,28,31,30,31,30,31,31,30,31,30};
这样写好像也行

[此贴子已经被作者于2016-3-25 15:07编辑过]

这样貌似可以，你可以试试。
#include <stdio.h>
int main(void)
{
    int day, year, month, sum, leap;
    printf("please input year,month,day\n");
    scanf("%d", &year);
    scanf("%d", &month);
    scanf("%d", &day);
    switch (month)
    {
    case 1:sum = 0;
        break;
    case 2:sum = 31;
        break;
    case 3:sum = 59;
        break;
    case 4:sum = 90;
        break;
    case 5:sum = 120;
        break;
    case 6:sum = 151;
        break;
    case 7:sum = 181;
        break;
    case 8:sum = 212;
        break;
    case 9:sum = 243;
        break;
    case 10:sum = 273;
        break;
    case 11:sum = 304;
        break;
    case 12:sum = 334;
        break;
    default:
        printf("data error");
        break;
        sum = sum + day;
        if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))
            leap = 1;
        else
            leap = 0;
        if (leap == 1 && month>2)
            sum += 1;
    }
    printf("It is the %dth day of %d year.\n", sum, year);
    return 0;
}