C++ 实现判断一个输入日期是星期几，是一年中的第几天

#include<iostream>
using namespace std;

struct time
{
int year;
int month;
int day;
unsigned int weekday;
};

void initialtime(time & t);//输入初始化时间
void Show(time & t);//显示时间信息
int Weekdaycount(time & t);//计算当日是星期几
int Daycount(time & t);//计算当日是第公元多少天
int Daysyearcount(time & t);//计算当日是该年的第多少天
bool isleapyear(time & t);//判断该年是不是闰年
bool check(time &t);//检查时间格式是否正确

int main()
{
time t;
initialtime(t);
Show(t);
return 0;
}

bool check(time &t)
{
if (t.year <= 0 || (t.month <= 0 || t.month>12) || t.day <= 0) return false;
else{
if ((t.month == 1 || t.month == 3 || t.month == 5 || t.month == 7
|| t.month == 8 || t.month == 10 || t.month == 12) && t.day > 31)return false;
else
{
if ((t.month == 4 || t.month == 6 || t.month == 9 || t.month == 11
) && t.day > 30)return false;
else
{
if (t.month == 2) {
if (isleapyear(t)) {
if (t.day > 29)return false; else return true;
}
else
{
if (t.day > 28)return false; else return true;
}
}
}
}
}
}
void initialtime(time & t)
{
cout << "Enter the time (year,month,day):\n";
cin >> t.year;
cin.get();
cin>> t.month;
cin.get();
cin >> t.day;
cin.get();
if (!check(t)){ cout << "Try again:\n"; initialtime(t); }
else
t.weekday = Weekdaycount(t);
}
void Show(time & t)
{
cout << "Year: " << t.year << "\t";
cout << "Month: " << t.month << "\t";
cout << "Day: " << t.day << "\t";
cout << "Weekday: " << t.weekday << endl;
cout << "This is a ";
if (isleapyear(t))cout << "leap"; else cout << "nonleap";
cout << " year.\n";
cout << "Today is the " << Daysyearcount(t) << " days of the year.\n";
}
int Weekdaycount(time & t)
{
return Daycount(t) % 7;
}
int Daycount(time & t)
{
int days = 0;
days = (t.year - 1) * 365 + (t.year - 1) / 4 - (t.year - 1) / 100
+ (t.year - 1) / 400 + Daysyearcount(t);
return days;
}
bool isleapyear(time & t)
{
if (t.year % 4 == 0 && t.year % 100 != 0) return true;//年是四的倍数而且不是100的倍数，是闰年
if (t.year % 400 == 0)return true;
else return false;
}
int Daysyearcount(time & t)
{
int days = 0;
int mtemp = t.month - 1;
while (mtemp > 0)
{
switch (mtemp)
{
case(1) :
case(3) : 
case(5) : 
case(7) : 
case(8) : 
case(10) : 
case(12) :
days += 31; break;
case(4):
case(6):
case(9): 
case(11):
days += 30; break;
case(2) :
days += 28; break;
default:
break;
}
--mtemp;
}
if (isleapyear(t))++days;//如果是闰年，再加上一天
return days+t.day;//返回计算的天数加上当月的天数
}

 
以上是以独立函数实现的代码，下次改进用类的表达修改一下！