用C语言编程:某人三天打渔两天晒网，假设他从1990年1月1日开始打渔三天，然后晒网两天，请编程回答任意的一天他在打渔还是晒网。 A boy works for 3 days while has a 2 days off. If he is working on 1st, Jan, 1990, then for a date entered from the keyboard, please write a program to determine what the boy is doing, working or resting? Examples of input and output: 1)Input: 1990-01-05 Output: He is having a rest. 2)Input: 1990-01-07 Output: He is working. 3)Input: 1990-01-33 Output: Invali input. ***输入数据格式***d："%4d-%2d-%2d" ***输出数据格式***："Invalid input."或"He is having a rest." 或"He is working."

#include <stdio.h>

int main() {
    int year, month, day;
    int days;
    printf("Please enter a date (yyyy-mm-dd): ");
    if (scanf("%d-%d-%d", &year, &month, &day) != 3) {
        printf("Invalid input.\n");
        return 0;
    }
    switch (month) {
        case 1: case 3: case 5: case 7: case 8: case 10: case 12:
            days = 31;
            break;
        case 4: case 6: case 9: case 11:
            days = 30;
            break;
        case 2:
            if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                days = 29;
            } else {
                days = 28;
            }
            break;
        default:
            printf("Invalid input.\n");
            return 0;
    }
    if (day > days) {
        printf("Invalid input.\n");
        return 0;
    }
    int days_since_1990 = 0;
    for (int y = 1990; y < year; y++) {
        if ((y % 4 == 0 && y % 100 != 0) || y % 400 == 0) {
            days_since_1990 += 366;
        } else {
            days_since_1990 += 365;
        }
    }
    for (int m = 1; m < month; m++) {
        switch (m) {
            case 1: case 3: case 5: case 7: case 8: case 10: case 12:
                days_since_1990 += 31;
                break;
            case 4: case 6: case 9: case 11:
                days_since_1990 += 30;
                break;
            case 2:
                if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0) {
                    days_since_1990 += 29;
                } else {
                    days_since_1990 += 28;
                }
                break;
        }
    }
    days_since_1990 += day - 1;
    int remainder = days_since_1990 % 5;
    if (remainder < 3) {
        printf("He is working.\n");
    } else {
        printf("He is having a rest.\n");
    }
    return 0;
}