有功能选择的万年历C语言实现代码

以下是一个带有功能选择的万年历C语言实现代码，可以选择查看指定年份、指定月份、以及指定日期的日历：

#include <stdio.h>

// 计算某年某月的天数
int month_days(int year, int month)
{
    int days = 0;
    switch (month) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
            days = 31;
            break;
        case 2:
            if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
                days = 29;  // 闰年2月有29天
            }
            else {
                days = 28;  // 平年2月有28天
            }
            break;
        default:
            days = 30;
            break;
    }
    return days;
}

// 输出日历表头
void print_calendar_header()
{
    printf("日\t一\t二\t三\t四\t五\t六\n");
}

// 输出日历表格
void print_calendar(int year, int month, int week_day)
{
    int i, j, days;
    days = month_days(year, month);
    for (i = 0; i < week_day; ++i) {
        printf("\t");  // 输出1号前的空格
    }
    for (i = 1, j = week_day; i <= days; ++i, ++j) {
        printf("%d\t", i);
        if (j % 7 == 6) {
            printf("\n");  // 每输出7个数字换行
        }
    }
    printf("\n");
}

int main()
{
    int year, month, day, days, i, week_day, choice;
    printf("请选择功能：\n");
    printf("1. 查看指定年份的日历\n");
    printf("2. 查看指定月份的日历\n");
    printf("3. 查看指定日期的日历\n");
    scanf("%d", &choice);
    switch (choice) {
        case 1:
            printf("请输入年份：\n");
            scanf("%d", &year);
            printf("请输入要查看的月份（1-12）：\n");
            scanf("%d", &month);
            week_day = (year - 1) * 365 + (year - 1) / 4 - (year - 1) / 100 + (year - 1) / 400;
            for (i = 1; i < month; ++i) {
                week_day += month_days(year, i);
            }
            week_day %= 7;
            printf("%d年%d月的日历如下：\n", year, month);
            print_calendar_header();
            print_calendar(year, month, week_day);
            break;
        case 2:
            printf("请输入年份：\n");
            scanf("%d", &year);
            printf("请输入要查看的月份（1-12）：\n");
            scanf("%d", &month);
            week_day = (year - 1) * 365 + (year - 1) / 4 - (year - 1) / 100 + (year - 1) / 400;
            for (i = 1; i < month; ++i) {
                week_day += month_days(year, i);
            }
            week_day %= 7;
            printf("%d年%d月的日历如下：\n", year, month);
            print_calendar_header();
            print_calendar(year, month, week_day);
            break;
        case 3:
            printf("请输入日期（格式：年-月-日）：\n");
            scanf("%d-%d-%d", &year, &month, &day);
            week_day = (year - 1) * 365 + (year - 1) / 4 - (year - 1) / 100 + (year - 1) / 400;
            for (i = 1; i < month; ++i) {
                week_day += month_days(year, i);
            }
            week_day %= 7;
            printf("%d年%d月%d日的日历如下：\n", year, month, day);
            print_calendar_header();
            print_calendar(year, month, week_day);
            break;
        default:
            printf("无效的输入！\n");
            break;
    }
    return 0;
}

该程序通过输入功能选择以及相应的参数，可以选择查看指定年份、指定月份、以及指定日期的日历。具体实现中，使用了多个函数来实现日历表的输出，并且使用了 `switch` 语句来根据用户选择进行不同的操作。