C 语言实现万年历
项目介绍
万年历（Perpetual Calendar）是可以使用很多年的日历，通常设计成可以计算未来某一日期在星期中的日子。
本项目使用纯 C 语言，实现一 个可以生成任意年份的万年历程序。该程序接收一个年份作为输入，然后打印出该年份各个月的日历。就如同我们平常看到的日历一样，每个月当中每天对应的星期均可查看。要求格式整齐，星期对照直观，并支持中英文输出。
代码思路
首先构思整个需求的思路，即接收一个年份，然后打印该年各个月的日历，其难点在于如何知道每个月的第一天是星期几，后面的天数即可依次循环打印即可。
本项目需要知道的其余几个小技术点和易出错点：
- 判断闰年，这里判断不对易出错，方法是能被 4 整除并且能被 100 整除，或者是直接能被 400 整除。
- 能判断出某月某天是这一年的第几天，方法是把这个月前面的天数加上这个月的天数。
- 如何知道每个月多少天，这个除了二月其余月是固定的，可以提前写好（二月可以定 28 天也可以 29 天），特殊判定这年是否是闰年，来决定是否单独加一天或减一天。
- 格式问题，熟练使用宏定义、switch 语句判断即可，做好实际数字与英文的对应打印。
代码实现
完整工程代码可以在 GitHub 仓库获取。
calendar.c
#include <stdio.h>
#define Mon 1
#define Tues 2
#define Wed 3
#define Thur 4
#define Fri 5
#define Sat 6
#define Sun 0
#define January_days 31
#define February_days 28
#define March_days 31
#define April_days 30
#define May_days 31
#define June_days 30
#define July_days 31
#define August_days 31
#define September_days 30
#define October_days 31
#define November_days 30
#define December_days 31
#define first1month (January_days)
#define first2month (first1month + February_days)
#define first3month (first2month + March_days)
#define first4month (first3month + April_days)
#define first5month (first4month + May_days)
#define first6month (first5month + June_days)
#define first7month (first6month + July_days)
#define first8month (first7month + August_days)
#define first9month (first8month + September_days)
#define first10month (first9month + October_days)
#define first11month (first10month + November_days)
char *month_names_en[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
char *month_names_zh[] = {"一月", "二月", "三月", "四月", "五月", "六月", "七月", "八月", "九月", "十月", "十一月", "十二月"};
int known_weekday = Tues;
int known_year = 1901;
int konwn_month = 1;
int known_day = 1;
int day_count(int month)
{
switch(month)
{
case 1: return 0; break;
case 2: return first1month; break;
case 3: return first2month; break;
case 4: return first3month; break;
case 5: return first4month; break;
case 6: return first5month; break;
case 7: return first6month; break;
case 8: return first7month; break;
case 9: return first8month; break;
case 10: return first9month; break;
case 11: return first10month; break;
case 12: return first11month; break;
}
}
char *get_month_name(int month)
{
if (month < 1 || month > 12) {
return "";
}
#ifdef PRINT_IN_CHINESE
return month_names_zh[month-1];
#else
return month_names_en[month-1];
#endif
}
/* 按格式打印某年某月名称 */
void print_month_header(int month, int year)
{
#ifdef PRINT_IN_CHINESE
printf("%15d年 %s \n", year, get_month_name(month));
#else
printf("%17s %d \n", get_month_name(month), year);
#endif
}
/* 按格式打印星期名称 */
void print_week_header()
{
#ifdef PRINT_IN_CHINESE
printf(" %-6s%-6s%-6s%-6s%-6s%-6s%-6s\n","日", "一", "二", "三", "四", "五", "六");
#else
printf("%-5s%-5s%-5s%-5s%-5s%-5s%-5s\n","Sun.", "Mon.", "Tue.", "Wed.", "Thu.", "Fri.", "Sat.");
#endif
}
/* 计算该年该月份与已知日子之间的距离天数 */
int date_distance_count(int month, int year)
{
int leap_year_count = 0;
int i;
int distance;
if (year > known_year)
{
for (i=known_year; i<year; i++)
{
if(((i%4 == 0) && (i%100 != 0) ) || (i%400 == 0))
{
leap_year_count++;
}
}
if (month > 2)
{
if(((year%4 == 0) && (year%100 != 0) ) || (year%400 == 0))
{
leap_year_count++;
}
}
}
else {
if (year == known_year)
{
if (month > 2)
{
leap_year_count = 1;
}
}
}
distance = (year - known_year) * 365 + leap_year_count + day_count(month);
return distance;
}
/* 确定该月份第一天是星期几 */
int makesure_firstday_weekday(int month, int year)
{
int date_distance = 0;
int weekday;
date_distance = date_distance_count(month, year);
weekday = (known_weekday + date_distance) % 7;
return weekday;
}
/* 依次打印出该月份的日子 */
void print_in_turn(int month, int firstday, int year)
{
int i = 1;
int weekday;
switch(firstday)
{
case Sun:
break;
case Mon:
printf("%-5s", "");
break;
case Tues:
printf("%-10s", "");
break;
case Wed:
printf("%-15s", "");
break;
case Thur:
printf("%-20s", "");
break;
case Fri:
printf("%-25s", "");
break;
case Sat:
printf("%-30s", "");
break;
}
switch(month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
{
for(i=0; i<31; i++)
{
weekday = (firstday + i) % 7;
printf("%3d ", i+1);
if(weekday == Sat)
{
printf("\n");
}
}
break;
}
case 2:
{
if(((year%4 == 0) && (year%100 != 0) ) || (year%400 == 0)) /*闰年*/
{
for(i=0; i<29; i++)
{
weekday = (firstday + i) % 7;
printf("%3d ", i+1);
if(weekday == Sat)
{
printf("\n");
}
}
break;
}
else /*平年*/
{
for(i=0; i<28; i++)
{
weekday = (firstday + i) % 7;
printf("%3d ", i+1);
if(weekday == Sat)
{
printf("\n");
}
}
break;
}
}
case 4:
case 6:
case 9:
case 11:
{
for(i=0; i<30; i++)
{
weekday = (firstday + i) % 7; /*计算该天是星期几*/
printf("%3d ", i+1);
if(weekday == Sat)
{
printf("\n"); /*如果是星期六，则换行*/
}
}
break;
}
}
}
void print_date(int month, int year)
{
int firstday;
firstday = makesure_firstday_weekday(month, year);
print_in_turn(month, firstday, year);
printf("\n");
}
void print_month(int month, int year)
{
print_month_header(month, year);
print_week_header();
print_date(month, year);
printf("\n\n");
}
void print_calendar(int year)
{
int i;
for(i=1; i<=12; i++)
{
print_month(i, year);
}
}
int main()
{
int year;
printf("请输入年份：year = ");
scanf("%d", &year);
printf("\n");
while(year < 1902) {
printf("请输入大于1901的年份\n");
printf("请输入年份：year = ");
scanf("%d", &year);
printf("\n");
}
print_calendar(year);
return 0;
}
编译运行
打开终端，切换到 calendar.c 文件所在目录，执行下面命令编译程序：
gcc calendar.c -o calendar
如果你从 GitHub 下载了完整工程，那么可以直接执行 make 编译：
$ make
默认为英文输出，如果需要中文输出，可以在编译时添加 PRINT_IN_CHINESE 宏定义：
$ make CFLAGS=-DPRINT_IN_CHINESE
或者直接修改 Makefile 文件，添加 CFLAGS += -D PRINT_IN_CHINESE 宏定义。
编译完成后，执行程序 ./calendar，输入要生成的年份（例如 2024），日历输出如下：
$ ./calendar
请输入年份：year = 2024
January 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
February 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29
March 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31
April 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30
May 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
June 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30
July 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
August 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31
September 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30
October 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
November 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
December 2024
Sun. Mon. Tue. Wed. Thu. Fri. Sat.
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31