输入年份和月份打印当月日历

/*
    QQ：778138708
    date:2020-5-14
    输入年份和月份，打印当月日历
 
*/
/*
    日期转换为星期的方法
    W= (d+2*m+3*(m+1)/5+y+y/4-y/100+y/400+1)%7
    在公式中d表示日期中的日数，m表示月份数，y表示年数
    把一月和二月看成是上一年的十三月和十四月，例：如果是2004-1-10则换算成：2003-13-10来代入公式计算。
*/
#include <stdio.h>
int weekNum(int year, int month, int day);
int isLeap(int year);
void printBlank(int n);
int main(void)
{
    int year, month;
    int leap, days;
    int i, firstDateWeek, dateWeek;
    int tab[2][13] = {{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
        {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}};
    
    printf("请输入一个年份(例如:2020):");
    scanf("%d", &year);
    printf("请输入一个月份(1-12的数字):");
    scanf("%d", &month);
    
    leap = isLeap(year);
    days = tab[leap][month];    //每个月的总天数
    
    printf("		%d年%d月
", year, month);
    printf("--------------------------
");
    printf("日	一	二	三	四	五	六
");
    
    //计算1号的星期数
    firstDateWeek = weekNum(year, month, 1);
    printBlank(firstDateWeek);      //每个月日历前的空白
    
    //开始打印日期
    for (i = 1; i <= days; i++) {
        printf("%d	", i);
        dateWeek = weekNum(year, month, i);
        if (dateWeek == 6) {
            printf("
");
        }
    }
    
    printf("
");
    
    return 0;
}
//日期转换为星期
int weekNum(int year, int month, int day)
{
    int week;
    
    if (month == 1 || month == 2) {
        year =year - 1;
        month = 12 + month;
    }
    week = (day + 2 * month + 3 * (month + 1) / 5 + year + year / 4 - year / 100 + year / 400 + 1) % 7;
    
    return week;
}
//判断闰年
int isLeap(int year)
{
    int leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    
    return leap;
}
//打印1号之前的空白
void printBlank(int n)
{
    int i;
    
    for (i = 0; i < n; i++)
    {
        printf("	");
    }
}

方法二

#include <stdio.h>
#include <stdbool.h>

#define START_DAY_FOR_JAN_1_1800 3

void printMonth(int year, int month);
void printMonthTitle(int year, int month);
void printMonthBody(int year, int month);
int getStartDay(int year, int month);
int getTotalNumberOfDays(int year, int month);
int getNumberOfDaysInMonth(int year, int month);
bool isLeapYear(int year);
int main(void)
{
    int year, month;

    printf("请输入一个年份:(例如:2020):");
    scanf("%d", &year);

    printf("请输入一个月份:(1-12的数字):");
    scanf("%d", &month);

    printMonth(year, month);

    return 0;
}

//打印相应年份和月份的日历
void printMonth(int year, int month)
{
    //打印日历的开头
    printMonthTitle(year, month);

    //打印日历内容
    printMonthBody(year, month);
}

//打印日历的开头
void printMonthTitle(int year, int month)
{
    printf("		%d年%d月
",year,month);
    printf("--------------------------
");
    printf("日	一	二	三	四	五	六
");

}

//打印日历的内容
void printMonthBody(int year, int month)
{
    int startDay = getStartDay(year, month);
    int i;

    //在当月的第一天前面加上若干个空格
    for (i = 0; i < startDay; i++)
    {
        printf("	");
    }
    
    for (i = 1; i <= getNumberOfDaysInMonth(year, month); i++)
    {
        printf("%2d	", i);
        //星期六换行
        if ((i + startDay) % 7 == 0)
        {
            printf("
");
        }
    }
    printf("
");
}

//返回某月第一天是星期几
int getStartDay(int year, int month)
{
    return (START_DAY_FOR_JAN_1_1800 + getTotalNumberOfDays(year, month)) % 7;

}
//返回从1800年1月1日至year年month月1日之间的天数
int getTotalNumberOfDays(int year, int month)
{
    int totalDays = 0;
    int i;
    for (i = 1800; i < year; i++)
    {
        //闰年问题
        if (isLeapYear(i))
        {
            totalDays += 366;
        }
        else
        {
            totalDays += 365;
        }
    }
    
    for (i = 1; i < month; i++)
    {
        totalDays += getNumberOfDaysInMonth(year, i);
    }

    return totalDays;
}
//返回每个月的天数
int getNumberOfDaysInMonth(int year, int month)
{
    int days;

    if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
    {
        days = 31;
    }
    else if (month == 4 || month == 6 || month == 9 || month == 11)
    {
        days = 30;
    }
    else if (month == 2)
    {
        //闰年问题
        days = isLeapYear(year)?29:28;
    }
    else
    {
        days = 0;
    }

    return days;
}

//判断是否是闰年
bool isLeapYear(int year)
{
    return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
}