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正文
这个例子在前例的基础上添加了如下内容：
- 为SavingsAccount类添加一个静态数据成员total，用来记录各个账户的总金额，并为其添加了相应的静态成员函数getTotal对其进行访问；
- 将getBalance，accumulate等不需要改变对象状态的成员函数声明为常成员函数；
- 对程序结构进行了调整：将SavingsAccount类从主函数所在的源函数分开，建立两个新的文件account.h和account.cpp分别存放SavingsAccount类的定义和实现；
代码如下：
//account.h
#ifndef _ACCOUNT_H_
#define _ACCOUNT_H_
class SavingsAccount {
public:
SavingsAccount(int date, int id, double rate);//构造函数
int getId() const { return id; }
double getBalance() const { return balance; }
double getRate() const { return rate; }
void show() const;
void deposit(int date, double amount);//取钱
void withdraw(int date, double amount);//存钱
void settle(int date);//结算利息，假设每年1月1号结算一次
static double getTotal() { return total; }
private:
int id;
double balance;
double rate;
int lastDate;
double accumulation;//计算账户余额的按日累计值
//记录一笔账，date为日期，amount为金额
static double total;
void record(int date, double amount);
double accumulate(int date) const {
return accumulation + (date - lastDate)*balance;
}
};
#endif
//account.cpp
#include "account.h"
#include <cmath>
#include <iostream>
using namespace std;
double SavingsAccount::total =0;
SavingsAccount::SavingsAccount(int date, int id, double rate)
:id(id), balance(0), rate(rate), lastDate(date), accumulation(0) {
cout << date << "\t#" << id << " is created" << endl;
}
void SavingsAccount::record(int date, double amount) {
accumulate(date);
lastDate = date;
amount = floor(amount * 100 + 0.5) / 100;//保留小数点后两位
balance = balance + amount;
total = total + amount;
cout << date << "\t#" << id << "\t" << balance << endl;
}
void SavingsAccount::deposit(int date, double amount) {
record(date, amount);
}
void SavingsAccount::withdraw(int date, double amount) {
if (amount > getBalance())
cout << "Error: not enough money" << endl;
else
record(date, -amount);
}
void SavingsAccount::settle(int date) {
double interest = accumulate(date)*rate / 365;
if (interest != 0)
record(date, interest);
accumulation = 0;
}
void SavingsAccount::show() const {
cout << "#" << id << "\tBalance:" << balance << endl;
}
//test.cpp
#include "account.h"
#include <iostream>
using namespace std;
int main() {
//建几个账户
SavingsAccount sa0(1, 21325302, 0.015);
SavingsAccount sa1(1, 58320212, 0.015);
//几笔账目
sa0.deposit(5, 5000);
sa1.deposit(25, 100000);
sa0.deposit(45, 5500);
sa1.withdraw(60, 4000);
//假设开户90天到了银行的计息日，结算所有账户的年息
sa0.settle(90);
sa1.settle(90);
//输出各个账户的信息
sa0.show();
cout << endl;
sa1.show();
cout << endl;
cout << "Total:" << SavingsAccount::getTotal() << endl;
return 0;
}
Here is the result
