原题目：某人从2010年1月1日起开始“三天打鱼两天晒网”，问这个人在以后的某一天中是“打鱼”还是“晒网”。

以下是程序源代码，初学者可能在很多地方不是很完善。

#include<stdio.h>
struct fish{};
int year, month, day;
int i;//闰年
int j = 0;//闰年个数
int k = 0;//平年个数
int y_s, m_s;//年月差
int t = 0;//总日差
int r = 0;//判断打渔晒网
 
 
//判断年份
int judge() {
    //判断年分输入是否正确
    if (year < 2010) {
        printf_s("year error!\n");
        return 0;
    } else {
        //判断闰年
        if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0){
            i = 1;
        } else {
            i = 0;
        }
    }
    return 1;
}

//计算年份
void count() {
    j = (year - 2010) / 4;//计算闰年个数
    k = (year - 2010) - j;//计算平年个数
    y_s = 366 * j + 365 * k;//计算年份差
}
//判断月份差
int j_m() {
    judge();
    if (i = 1) {
        //计算月份差
        switch (month) {
            case 1:
                m_s = 0;
                break;
            case 2:
                m_s = 31;
                break;
            case 3:
                m_s = 59;
                break;
            case 4:
                m_s = 90;
                break;
            case 5:
                m_s = 120;
                break;
            case 6:
                m_s = 151;
                break;
            case 7:
                m_s = 181;
                break;
            case 8:
                m_s = 212;
                break;
            case 9:
                m_s = 243;
                break;
            case 10:
                m_s = 273;
                break;
            case 11:
                m_s = 304;
                break;
            case 12:
                m_s = 334;
                break;
            default:
                printf_s("month error!\n");
                return 0;
        }
    } else if (i = 0) {
        //计算月份差
        switch (month) {
            case 1:
                m_s = 0;
                break;
            case 2:
                m_s = 31;
                break;
            case 3:
                m_s = 58;
                break;
            case 4:
                m_s = 89;
                break;
            case 5:
                m_s = 119;
                break;
            case 6:
                m_s = 150;
                break;
            case 7:
                m_s = 180;
                break;
            case 8:
                m_s = 211;
                break;
            case 9:
                m_s = 242;
                break;
            case 10:
                m_s = 272;
                break;
            case 11:
                m_s = 303;
                break;
            case 12:
                m_s = 333;
                break;
            default:
                printf_s("month error!\n");
                return 0;
        }
    }
    return 1;
}
//判断打渔晒网
void reckon() {
    t = y_s + m_s + day;
    r = t % 5;
    //判断打渔晒网
    switch (r) {
        case 0:
            printf_s("今天晒网\n");
            break;
        case 1:
        case 2:
        case 3:
            printf_s("今天打渔\n");
            break;
        case 4:
            printf_s("今天晒网\n");
            break;
    }
}
//判断日子
void j_d() {
    if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12  ) {
        if (day<1||day>31) {
            printf_s("day error!\n");
        } else {
            reckon();
        }
    } else {
        if (month == 4 || month == 6 || month == 9 || month == 11) {
            if (day<1 || day>30) {
                printf_s("day error!\n");
            } else {
                reckon();
            }
        } else {
            if (i=1) {
                if (day<1 || day>29) {
                    printf_s("day error!\n");
                } else {
                    reckon();
                }
            } else {
                if (day<1 || day>28) {
                    printf_s("day error!\n");
                } else {
                    reckon();
                }
            }
        }
    }
}

//主函数
int main() {
    int choose=1;
    while (choose) {
        printf_s("请输入一个日期（在2010.1.1以后的日期）并以英文逗号隔开：\n");
        scanf_s("%d,%d,%d", &year, &month, &day);
        if (judge()) {
            if (j_m()) {
                j_d();
            }
        }
        printf_s("继续请输入1，结束请输入0：\n");
        scanf_s("%d",&choose);
    }
    return 0;
}

最终效果图：