创建一个Date类

头文件：1 Data class.h

#ifndef I_DATE_ED
#define I_DATE_ED

#include 
#include 
using namespace std;
// year应当是1800到2200之间的整数；
// month必须是1到12之间的整数；
// day必须是1到给定、月的天数之间的整数；
class Date
{
	int year, month, day;
public:
	Date() {month = 1; day = 1; year = 1800;}
	Date(int, int, int);
	bool isvalid();		// 判断Date是否合法
	void readinto();	// 用读入的month、day和year设置这个Date的值
	Date next();		// 返回Date之后的Date
	Date previous();	// 返回Date之前的Date
	string dayofweek();	// 返回这个Date是星期几
	friend ostream& operator<<(ostream&, Date&);
};

Date::Date(int monthln, int dayln, int yearln)
{
	month = monthln;
	day = dayln;
	year = yearln;
}

bool Date::isvalid()
{
	if (year < 1800 || year > 2200)
		return false;
	else 
		switch(month){
		case 1: case 3: case 5: case 7:
		case 8: case 10: case 12:
			if (day < 1 || day > 31) return false;
		case 4: case 6: case 9: case 11:
			if (day < 1 || day > 30) return false;
		case 2:
			if ((year%4 == 0 && year%100 != 0) || year%400 == 0)
				if (day < 1 || day >29) return false;
				else ;
			else if (day < 1 || day > 28)
				return false;
		default:
			return true;
	}
}

void Date::readinto()
{
	cout << "Please input \"month day, year\":\n";
	cin >> month >> day >> year;
}

Date Date::next()
{
	switch(month){
	case 1: case 3: case 5: case 7:
	case 8: case 10:
		if (day != 31) {day++; break;}
		else {day = 1; month++; break;}
	case 4: case 6: case 9: case 11:
		if (day != 30) {day++; break;}
		else {day = 1; month++; break;}
	case 2:
		if ((year%4 == 0 && year%100 != 0) || year%400 == 0)
			if (day != 29) {day++; break;}
			else {day = 1; month++; break;}
		else if (day != 28) {day++; break;}
		else {day = 1; month++; break;}
	case 12:
		if (day != 31) {day++; break;}
		else if (year <= 2200 && year >= 1800)
			{day = 1; month = 1; year++; break;}
		else
			cout << "Out of the Date!";
	}
	return *this;
}

Date Date::previous()
{
	switch(month){
	case 2: case 4: case 6: case 8:
	case 9: case 11:
		if (day != 1) {day--; break;}
		else {day = 31; month--; break;}
	case 5: case 7: case 10: case 12:
		if (day != 1) {day--; break;}
		else {day = 30; month--; break;}
	case 3:
		if ((year%4 == 0 && year%100 != 0) || year%400 == 0)
			if (day != 1) {day--; break;}
			else {day = 29; month--; break;}
		else if (day != 1) {day--; break;}
		else {day = 28; month--; break;}
	case 1:
		if (day != 1) {day--; break;}
		else if (year <= 2200 && year >= 1800)
			{day = 31; month = 12; year--; break;}
		else
			cout << "Out of the Date!";
	}
	return *this;
}

// 算法公式： Week=(Day + 2*Month + 3*(Month+1)/5 + Year + Year/4 - Year/100 + Year/400) % 7
//　　		（其中的Year是4位数的，如2009。“%”号是等式除7取余数）
// 该式对应的与蔡勒公式有点区别：“0”为星期1，……，“6”为星期日！
// 某年的1、2月要看作上一年的13、14月来计算，比如2003年1月1日要看作2002年的13月1日来计算
string Date::dayofweek()
{
	int myweek;
	if (month == 1 || month == 2){
		year--; month += 12;
	}
	myweek = (day + 2*month + 3*(month+1)/5 + year + year/4 - year/100 + year/400) % 7;
	if (month == 13 || month == 14){
		year++; month -= 12;
	}
	switch(myweek){
	case 0: return "Monday";
	case 1: return "Tuesday";
	case 2: return "Wednesday";
	case 3: return "Thursday";
	case 4: return "Friday";
	case 5: return "Saturday";
	case 6: return "Sunday";
	}
}

ostream& operator<<(ostream& out, Date& ate)
{
	out << ate.month << ' ' << ate.day << ", "<< ate.year;
	return out;
}

#endif

驱动程序：data.cpp

#include "1 Date class.h"
int main()
{
	Date dat1;
	Date dat2(2, 28, 1900);		// 不是闰年
	Date dat3(12, 31, 2008);
	if (dat1.isvalid())
		cout << "dat1 = " << dat1 << endl;
	else
		return 0;
	if (dat2.isvalid())
		cout << "dat2 = " << dat2 << endl;
	else
		return 0;
	cout << "dat3 = " << dat3 << endl << endl;

	dat1.readinto();
	cout << "dat1 = " << dat1 << endl << endl;

	cout << "dat1.next() = " << dat1.next() << endl
		 << "dat2.next() = " << dat2.next() << endl
		 << "dat3.next() = " << dat3.next() << endl;
	cout << "dat1.previous() = " << dat1.previous() << endl
		 << "dat2.previous() = " << dat2.previous() << endl
		 << "dat3.previous() = " << dat3.previous() << endl << endl;

	cout << dat1 << "	" << dat1.dayofweek() << endl
		 << dat2 << "	" << dat2.dayofweek() << endl
		 << dat3 << "	" << dat3.dayofweek() << endl;
	return 0;
}

这个类简单，所以把Date类的实现也放在头文件了，修改类实现时，vs检测不到头文件中的改动，必须改变.cpp的内容，才会重新编译……

只创建string对象可以 不包含头文件， 但这样不能执行cout << string;的操作；