实例：银行账户感悟

1.条件编译指令，可以避免重复包含的错误

#ifndef_ACCOUNT_H_    
#define_ACCOUNT_H_
.........
#endif_ACCOUNT_H_

2.合并时出了些问题，比如date和account的顺序导致dle找不到date
应将date放在前...算了！放弃你的想法
乖乖分成几个文件来写，要不然迟早玩完（微笑）

part1 account.h

//account.h
#ifndef __ACCOUNT_H__
#define __ACCOUNT_H__
#include "date.h"
#include 

class SavingsAccount { //储蓄账户类
private:
    std::string id;     //帐号
    double balance;     //余额
    double rate;        //存款的年利率
    Date lastDate;      //上次变更余额的时期
    double accumulation;    //余额按日累加之和
    static double total;    //所有账户的总金额

    //记录一笔帐，date为日期，amount为金额，desc为说明
    void record(const Date &date, double amount, const std::string &desc);
    //报告错误信息
    void error(const std::string &msg) const;
    //获得到指定日期为止的存款金额按日累积值
    double accumulate(const Date& date) const {
        return accumulation + balance * date.distance(lastDate);
    }
public:
    //构造函数
    SavingsAccount(const Date &date, const std::string &id, double rate);
    const std::string &getId() const { return id; }
    double getBalance() const { return balance; }
    double getRate() const { return rate; }
    static double getTotal() { return total; }

    //存入现金
    void deposit(const Date &date, double amount, const std::string &desc);
    //取出现金
    void withdraw(const Date &date, double amount, const std::string &desc);
    //结算利息，每年1月1日调用一次该函数
    void settle(const Date &date);
    //显示账户信息
    void show() const;
};

#endif //__ACCOUNT_H__

part2 date.h

//date.h
#ifndef __DATE_H__
#define __DATE_H__

class Date {    //日期类
private:
    int year;       //年
    int month;      //月
    int day;        //日
    int totalDays;  //该日期是从公元元年1月1日开始的第几天

public:
    Date(int year, int month, int day); //用年、月、日构造日期
    int getYear() const { return year; }
    int getMonth() const { return month; }
    int getDay() const { return day; }
    int getMaxDay() const;      //获得当月有多少天
    bool isLeapYear() const {   //判断当年是否为闰年
        return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
    }
    void show() const;          //输出当前日期
    //计算两个日期之间差多少天  
    int distance(const Date& date) const {
        return totalDays - date.totalDays;
    }
};

#endif //__DATE_H__

part3 account.cpp

//account.cpp
#include "account.h"
#include 
#include 
using namespace std;

double SavingsAccount::total = 0;

//SavingsAccount类相关成员函数的实现
SavingsAccount::SavingsAccount(const Date &date, const string &id, double rate)
    : id(id), balance(0), rate(rate), lastDate(date), accumulation(0) {
    date.show();
    cout << "\t#" << id << " created" << endl;
}

void SavingsAccount::record(const Date &date, double amount, const string &desc) {
    accumulation = accumulate(date);
    lastDate = date;
    amount = floor(amount * 100 + 0.5) / 100;   //保留小数点后两位
    balance += amount;
    total += amount;
    date.show();
    cout << "\t#" << id << "\t" << amount << "\t" << balance << "\t" << desc << endl;
}

void SavingsAccount::error(const string &msg) const {
    cout << "Error(#" << id << "): " << msg << endl;
}

void SavingsAccount::deposit(const Date &date, double amount, const string &desc) {
    record(date, amount, desc);
}

void SavingsAccount::withdraw(const Date &date, double amount, const string &desc) {
    if (amount > getBalance())
        error("not enough money");
    else
        record(date, -amount, desc);
}

void SavingsAccount::settle(const Date &date) {
    double interest = accumulate(date) * rate   //计算年息
        / date.distance(Date(date.getYear() - 1, 1, 1));
    if (interest != 0)
        record(date, interest, "interest");
    accumulation = 0;
}

void SavingsAccount::show() const {
    cout << id << "\tBalance: " << balance;
}

part4 main

//6_25.cpp
#include "account.h"
#include 
using namespace std;

int main() {
    Date date(2008, 11, 1); //起始日期
    //建立几个账户
    SavingsAccount accounts[] = {
        SavingsAccount(date, "S3755217", 0.015),
        SavingsAccount(date, "02342342", 0.015)
    };
    const int n = sizeof(accounts) / sizeof(SavingsAccount); //账户总数
    //11月份的几笔账目
    accounts[0].deposit(Date(2008, 11, 5), 5000, "salary");
    accounts[1].deposit(Date(2008, 11, 25), 10000, "sell stock 0323");
    //12月份的几笔账目
    accounts[0].deposit(Date(2008, 12, 5), 5500, "salary");
    accounts[1].withdraw(Date(2008, 12, 20), 4000, "buy a laptop");

    //结算所有账户并输出各个账户信息
    cout << endl;
    for (int i = 0; i < n; i++) {
        accounts[i].settle(Date(2009, 1, 1));
        accounts[i].show();
        cout << endl;
    }
    cout << "Total: " << SavingsAccount::getTotal() << endl;
    return 0;
}