C语言--万年历（只能显示阳历）

/*
 * File : calender.c
 * ----------------------
 * This program is used to generate a calender for a year entered by user.
 */

#include <stdio.h>

/*
 * Constants:
 * -----------
 * Days of the week are represented by the integers 0-6.
 * Month of the year are identified by the integers 1-12.
 */

#define Sunday 0
#define Monday 1
#define Tuesday 2
#define Wednesday 3
#define Thursday 4
#define Friday 5
#define Saturday 6

#define IsALeapYear(year) ((year % 4 == 0) && (year % 100 !=0)) || (year % 400 == 0)

/* Fuction prototypes */

void GiveInstructions();
int GetYear();
void PrintCalender(int year);
void PrintCalenderMonth(int year,int month);
char * MonthName(int month);
int FirstDayOfMonth(int year,int month);
int MonthDays(int year,int month);
void IndentFirstLine(int weekday);


/* Main Program */

void main()
{
    int year;

    GiveInstructions();
    year = GetYear();
    PrintCalender(year);
}


/*
 * Function: GiveInstructions
 * Usage: GiveInstructions();
 * ------------------------------------
 * This program prints out instructions to user.
 */

void GiveInstructions()
{
    printf("\n\n----------This program displays a calender for a full year.----------\n\n\n");
}


/*
 * Function: GetYear
 * Usage: year = GetYear();
 * -----------------------------------
 * This program will get a year from user.
 */

int GetYear()
{
    int year;

    printf("-----Please input a year:");
    scanf("%d",&year);
    printf("\n");
    return (year);
}


/*
 * Fuction: PrintCalender
 * Usage: PrintCalender(year);
 * ---------------------------------------
 * This program will print out a calender for a entire year.
 */

void PrintCalender(int year)
{
    int month;

    for (month = 1; month <= 12; month++) {
        PrintCalenderMonth(year, month);
    }
}


/*
 * Function: PrintCalenderMonth
 * Usage: PrintCalenderMonth(int year, int month)
 * -------------------------------------------------------------
 * This program will print out a calender for a entire month.
 */

void PrintCalenderMonth(int year, int month)
{
    int nDays,weekday,i;

    printf(" %s %d\n",MonthName(month),year);
    printf(" Su Mo Tu We Th Fr Sa\n");

    nDays = MonthDays(year,month);
    weekday = FirstDayOfMonth(year,month);

    IndentFirstLine (weekday);
    for (i = 1; i <= nDays; i++) {
        printf(" %2d",i);
        if (weekday == Saturday) printf("\n");
        weekday = (weekday + 1) % 7;
    }
    if (weekday != Sunday) printf("\n");
}


/*
 * Function: MonthName
 * Usage: char * MonthName(month)
 * ------------------------------------------
 * This program prints out the monthname.
 */

char * MonthName(int month)
{
    switch (month) {
        case 1: return ("January");
        case 2: return ("February");
        case 3: return ("March");
        case 4: return ("April");
        case 5: return ("May");
        case 6: return ("June");
        case 7: return ("July");
        case 8: return ("August");
        case 9: return ("September");
        case 10: return ("October");
        case 11: return ("November");
        case 12: return ("December");
        default: return ("Illegal month");
    }
}


/*
 * Function: FirstDayOfMonth
 * Usage: weekday = FirstDayOfMonth(year,month)
 * -------------------------------------------------------
 * This program returns the weekday of a month.
 */

int FirstDayOfMonth(int year,int month)
{
    int i,weekday,nDays;
    weekday = Monday;

    if (year > 1900) {
        for (i = 1900; i < year; i++) {
            weekday = (weekday + 365) % 7;
            if (IsALeapYear(i)) weekday = (weekday + 1) % 7;
        }
        for (i = 1; i < month; i++) {
            nDays = MonthDays(year,i);
            weekday = (weekday + nDays) % 7;
        }
    }
    else{
        for (i = 1900; i > year; i--) {
            weekday = (weekday - 365 + 7 * 53 ) % 7;
            if (IsALeapYear(i)) weekday = (weekday + 6) % 7;
        }
        for (i = 1; i < month; i++) {
            nDays = MonthDays(year,i);
            weekday = (weekday + nDays) % 7;
        }
    }
    return (weekday);
}


/*
 * Function: MonthDays
 * Usage: nDays = MonthDays(year,month)
 * -----------------------------------------------------
 * This program returns the number of days for a month.
 */

int MonthDays(int year,int month)
{
    switch (month) {
        case 2:
        if (IsALeapYear(year)) return (29);
        return (28);
        case 4:case 6:case 9:case 11:
        return (30);
        default : return (31);
    }
}


/*
 * Function: IndentFirstLine
 * Usage: IndentFirstLine(weekday)
 * --------------------------------------
 * This program prints out some blank spaces for the calender.
 */

void IndentFirstLine(int weekday)
{
    int i;

    for (i = 0; i < weekday; i++)
    {
        printf(" ");
    }
}


/* 参考《C语言的科学与艺术》*/