程序代码：

#include <stdio.h>

int is_leap(int year);//判断闰年

main()
{
    int year, month, day, d_day;
    int days[2][12]={{31,28,31,30,31,30,31,31,30,31,30,31},
                     {31,29,31,30,31,30,31,31,30,31,30,31}};//平年第0行，闰年第1行
    printf("输入起始日期：(yyyy-mm-dd)\n");
    scanf("%d-%d-%d", &year, &month, &day);
    printf("输入相隔天数：");
    scanf("%d", &d_day);
    
    while(d_day > days[is_leap(year)][month-1] - day)//剩余天数不够进位则停止循环
    {
        d_day -= days[is_leap(year)][month-1];
        month++;
        if(month == 13)
        {
            month = 1;
            year++;
        }
    }
    day += d_day;
    
    printf("%d-%02d-%02d\n", year, month, day);
    
}

int is_leap(int year)
{
    if(year % 4 != 0 || (year % 100 == 0 && year % 400 != 0))
        return 0;
    else
        return 1;   
}