该程序简单地输入一个年份（1901年之后的年份），随后程序输出该年份十二个月的日历。

#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  January_days+February_days
#define first3month  January_days+February_days+March_days
#define first4month  January_days+February_days+March_days+April_days
#define first5month  January_days+February_days+March_days+April_days+May_days
#define first6month  January_days+February_days+March_days+April_days+May_days+June_days
#define first7month  January_days+February_days+March_days+April_days+May_days+June_days \+July_days
#define first8month  January_days+February_days+March_days+April_days+May_days+June_days \+July_days+August_days
#define first9month  January_days+February_days+March_days+April_days+May_days+June_days \+July_days+August_days+September_days
#define first10month  January_days+February_days+March_days+April_days+May_days+June_days \+July_days+August_days+September_days+October_days
#define first11month  January_days+February_days+March_days+April_days+May_days+June_days \+July_days+August_days+September_days+October_days+November_daysint 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 * month_name(int month)
{switch(month){case 1:return "January";break;case 2:return "February";break;case 3:return "March";break;case 4:return "April";break;case 5:return "May";break;case 6:return "June";break;case 7:return "July";break;case 8:return "August";break;case 9:return "September";break;case 10:return "October";break;case 11:return "November";break;case 12:return "December";break;default:break;}
}*/char * month_name(int month)
{switch(month){case 1:return "一月";break;case 2:return "二月";break;case 3:return "三月";break;case 4:return "四月";break;case 5:return "五月";break;case 6:return "六月";break;case 7:return "七月";break;case 8:return "八月";break;case 9:return "九月";break;case 10:return "十月";break;case 11:return "十一月";break;case 12:return "十二月";break;default:break;}
}/*按格式打印某年某月名称*/
void first_line_print(int month, int year)
{//printf("%20s  %d  \n",month_name(month),year);printf("%8d年  %s  \n",year, month_name(month));
}/*按格式打印星期名称*/
void week_print()
{//printf("%-6s%-6s%-6s%-6s%-6s%-6s%-6s\n","Sun.", "Mon.", "Tues.", "Wed.", "Thur.", "Fri.", "Sat.");printf("%-3s%-3s%-3s%-3s%-3s%-3s%-3s\n","日", "一", "二", "三", "四", "五", "六");
}/*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++;		}}}elseif (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("%-3s","");break;case Tues:printf("%-6s","");break;case Wed:printf("%-9s","");break;case Thur:printf("%-12s","");break;case Fri:printf("%-15s","");break;case Sat:printf("%-18s","");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 date_print(int month, int year)
{int firstday;firstday = makesure_firstday_weekday(month, year);print_in_turn(month, firstday, year);printf("\n");
}void main_month(int month, int year)
{first_line_print(month, year);week_print();date_print(month, year);printf("\n\n");
}void main_calendar(int year)
{int i;for(i=1; i<=12; i++){main_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");}main_calendar(year);scanf(" ");return 0;
}

示例：