只有一个源文件main函数

代码有点多,有好几处可以简短,但是你知道的我比较懒!

这个代码最主要的是

int w;
        w = (day + 2 * month2 + 3 * (month2 + 1) / 5 + year2 + year2 / 4 - year2 / 100 + year2 / 400) % 7;/*基姆拉尔森计算公式*/     这个公式
#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>int isleap(int year);/*判断闰年*/
int validdate(int, int, int);/*判断日期是否正确*/
int tianshu(int year, int mouth, int day);/*天数总和*/
int whatday();/*计算当年第几天*/
int date_difference();/*日期差*/
int year_difference(int, int, int, int, int, int);/*年份天数差*/
int month_difference(int, int, int, int, int);/*月份天数差*/
int day_difference(int, int);/*日天数差*/
int yeardays(int);/*该年有多少天*/
int calculation_date();/*推算日期*/
int datemuch(int, int, int, int, int, int);/*判断哪个日期大*/int main(int argc, char* argv[])
{
    while (1)
    {
        printf("----------------日期计算器-----------------\n");
        printf("\t\t1.计算当年第几天\n");
        printf("\t\t2.计算两个日期差\n");
        printf("\t\t3.推算N天后日期\n");
        printf("\t\t0.退出\n");
        printf("请选择(0~~3选项):");
        int option;/*接收选项*/
        scanf("%d", &option);
        switch (option)
        {
        case 1://printf("计算当年第几天"); 
            whatday();
            break;
        case 2://printf("计算两个日期差");
            date_difference();
            break;
        case 3://printf("推算N天后日期"); 
            calculation_date();
            break;
        case 0:printf("谢谢使用!"); return 0;
        default:printf("输入的选项有误,请重新输入!\n");
        }
    }
}int isleap(int year)/*判断闰年*/
{
    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0))
    {
        return 1;
    }
    return 0;
}int validdate(int year, int month, int day)/*判断日期是否正确*/
{
    if (month < 1 || month>12) {
        printf("您输入的月份有误,应在(1~~12)之间!\n");
        return 0;
    }
    switch (month) {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12: if (day < 1 || day>31) {
        printf("您输入的日有误,应在 1~~~31 之间!\n");
        return 0;
    }break;
    case 4:
    case 6:
    case 9:
    case 11:if (day < 1 || day>30) {
        printf("您输入的日有误,应在 1~~~30 之间!\n");
        return 0;
    }break;
    case 2:if (isleap(year) && (day < 1 || day>29)) {
        printf("%d年是闰年,您输入的日有误,应在 1~~~29之间\n", year);
        return 0;
    }
          if (!isleap(year) && (day < 1 || day>28)) {
              printf("%d年是平年,您输入的日有误,应在 1~~~28之间\n", year);
              return 0;
          }break;
    }
    return 1;
}int tianshu(int year, int month, int day) /*天数总和*/
{
    int num[11] = { 31,28,31,30,31,30,31,31,30,31,30 };
    int days = day;
    int i;
    for (i = 0; i < month - 1; i++) {
        days += num[i];
    }
    if (isleap(year)) {
        days += 1;
    }
    return days;
}int whatday()/*计算当年第几天*/
{
    int year, month, day, days;
    printf("请输入年月日(xxxx-xx-xx,例:2022-3-3):");
    scanf("%d-%d-%d", &year, &month, &day);
    if (!validdate(year, month, day))
    {
        printf("您输入的日期有误!\n");
        return 0;
    }
    days = tianshu(year, month, day);
    printf("%d-%d-%d是%d年的第%d天。\n", year, month, day, year, days);
    printf("距离%d年结束还有%d天。\n", year, yeardays(year) - days);
}int date_difference()/*日期差*/
{
    int year1, month1, day1, year2, month2, day2;
    do {
        printf("请输入第一个日期xxxx-xx-xx(例:2022-3-3):");
        scanf("%d-%d-%d", &year1, &month1, &day1);
    } while (!validdate(year1, month1, day1));/*判断日期是否正确*/    do {
        printf("请输入第二个日期xxxx-xx-xx(例:2022-4-3):");
        scanf("%d-%d-%d", &year2, &month2, &day2);
    } while (!validdate(year2, month2, day2));/*判断日期是否正确*/    datemuch(year1, month1, day1, year2, month2, day2);
}int year_difference(int year1, int month1, int day1, int year2, int month2, int day2)/*年份天数差*/
{
    int days = 0, start, end, startdays, enddays;
    if (year1 > year2)
    {
        start = year2;
        end = year1;
        startdays = tianshu(year2, month2, day2);
        enddays = tianshu(year1, month1, day1);
    }
    else
    {
        start = year1;
        end = year2;
        startdays = tianshu(year1, month1, day1);
        enddays = tianshu(year2, month2, day2);
    }
    for (int i = start; i <= end; i++)
    {
        if (i == start)
        {
            days += yeardays(start) - startdays;
        }
        else if (i == end)
        {
            days += enddays;
        }
        else
        {
            days += yeardays(i);
        }
    }
    return days;
}int month_difference(int year1, int month1, int month2, int day1, int day2)/*月份天数差*/
{
    int days = tianshu(year1, month1, day1) - tianshu(year1, month2, day2);
    return days > 0 ? days : -days;
}int day_difference(int day1, int day2)/*日天数差*/
{
    return (day1 - day2 > 0 ? day1 - day2 : day2 - day1);
}int yeardays(int year)/*该年有多少天*/
{
    return isleap(year) ? 366 : 365;
}int datemuch(int year1, int month1, int day1, int year2, int month2, int day2)/*判断哪个日期大*/
{
    if (year1 == year2)
    {
        if (month1 == month2)
        {
            if (day1 == day2)
            {
                printf("%d年%d月%d日和%d年%d月%d日是同一个日期,相差0天!\n", year1, month1, day1, year2, month2, day2);
            }
            else
            {
                printf("%d年%d月%d日和%d年%d月%d日相差%d天!\n", year1, month1, day1, year2, month2, day2, day_difference(day1, day2));
            }
        }
        else
        {
            printf("%d年%d月%d日和%d年%d月%d日相差%d天!\n", year1, month1, day1, year2, month2, day2, month_difference(year1, month1, month2, day1, day2));
        }
    }
    else
    {
        printf("%d年%d月%d日和%d年%d月%d日相差%d天!\n", year1, month1, day1, year2, month2, day2, year_difference(year1, month1, day1, year2, month2, day2));
    }
}int calculation_date()/*推算N天后日期*/
{
    int year1, month1, day1, days, year, month, day;
    int num[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };
    do {
        printf("请输入要推算的日期(xxxx-xx-xx,例:2022-3-3):");
        scanf("%d-%d-%d", &year1, &month1, &day1);
    } while (!validdate(year1, month1, day1));
    printf("请输入推算的天数(负数向前计算):");
    scanf("%d", &days);    if (days == 0)
    {
        year = year1;
        month = month1;
        day = day1;
    }
    else if (days > 0)
    {
        year = year1;
        month = month1;
        day = day1;        if (isleap(year))
        {
            num[2] = 29;
        }        for (int i = 1; i <= days; i++)
        {
            day += 1;
            if (day > num[month])
            {
                day = day - num[month];
                month++;
                if (month > 12)
                {
                    year++;
                    month = 1;
                    if (isleap(year))
                    {
                        num[2] = 29;
                    }
                    else
                    {
                        num[2] = 28;
                    }
                }
            }
        }
    }
    else
    {
        year = year1;
        month = month1;
        day = day1;        if (isleap(year))
        {
            num[2] = 29;
        }        days = -days;
        for (int i = 1; i <= days; i++)
        {
            day -= 1;
            if (day < 1)
            {
                month--;
                if (month < 1)
                {
                    year--;
                    month = 12;
                    if (isleap(year))
                    {
                        num[2] = 29;
                    }
                    else
                    {
                        num[2] = 28;
                    }
                }
                day = num[month];
            }
        }        int year2, month2;
        year2 = year;
        month2 = month;
        if ((month2 == 1) || (month2 == 2))
        {
            month2 += 12;
            year2--;
        }        int w;
        w = (day + 2 * month2 + 3 * (month2 + 1) / 5 + year2 + year2 / 4 - year2 / 100 + year2 / 400) % 7;/*基姆拉尔森计算公式*/
        switch (w)
        {
        case 0:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期一\n", year1, month1, day1, days, year, month, day); break;
        case 1:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期二\n", year1, month1, day1, days, year, month, day); break;
        case 2:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期三\n", year1, month1, day1, days, year, month, day); break;
        case 3:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期四\n", year1, month1, day1, days, year, month, day); break;
        case 4:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期五\n", year1, month1, day1, days, year, month, day); break;
        case 5:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期六\n", year1, month1, day1, days, year, month, day); break;
        case 6:printf("%d年%d月%d日%d天前的日期是%d年%d月%d日星期日\n", year1, month1, day1, days, year, month, day); break;
        }
        return 0;
    }    int year2, month2;
    year2 = year;
    month2 = month;
    if ((month2 == 1) || (month2 == 2))
    {
        month2 += 12;
        year2--;
    }    int w;
    w = (day + 2 * month2 + 3 * (month2 + 1) / 5 + year2 + year2 / 4 - year2 / 100 + year2 / 400) % 7;/*基姆拉尔森计算公式*/
    switch (w)
    {
    case 0:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期一\n", year1, month1, day1, days, year, month, day); break;
    case 1:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期二\n", year1, month1, day1, days, year, month, day); break;
    case 2:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期三\n", year1, month1, day1, days, year, month, day); break;
    case 3:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期四\n", year1, month1, day1, days, year, month, day); break;
    case 4:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期五\n", year1, month1, day1, days, year, month, day); break;
    case 5:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期六\n", year1, month1, day1, days, year, month, day); break;
    case 6:printf("%d年%d月%d日%d天后的日期是%d年%d月%d日星期日\n", year1, month1, day1, days, year, month, day); break;
    }
}