P493 brass

实现多态共有继承的两种方法

1 在派生类中重新定义基类的方法

2 使用虚方法

P493程序清单13.7使用的方法为在派生类中重新定义基类的方法

brass.h

#ifndef BRASS_H

#define BRASS_H

#include <string>

class Brass{

private:

    std::string fullName;  //客户姓名

    long acctNum;  //账号

    double balance;  //当前结余

public:

    Brass(const std::string & s="Nullbody",long an=-1,

          double bal=0.0);

    void Deposit(double amt);  //存款

    virtual void withdraw(double amt);  //取款

    double Balance() const; //显示余额

    virtual void ViewAcct() const;

    virtual ~Brass() {}

};

//Brass Plus Account Class

class BrassPlus:public Brass

{

private:

    double maxLoan;  //透支的上线

    double rate;  //透支贷款利率

    double owesBank;  //当前的透支额度

public:

    BrassPlus(const std::string &s="Nullbody",long an=-1,

              double bal=0.0,double ml=500,double r=0.11125);

    BrassPlus(const Brass &ba,double ml=500,

                              double r=0.11125);

    virtual void ViewAcct() const;

    virtual void withdraw(double amt);

    void ResetMax(double m){maxLoan=m;};

    void ResetRate(double r){rate=r;};

    void ResetOwes() {owesBank=0;};

};

#endif // BRASS_H

main.cpp

#include <iostream>

#include "brass.h"

using namespace std;

//formatting stuff

typedef std::ios_base::fmtflags format;

typedef std::streamsize precis;

format setFormat();

void restore(format f,precis p);

//Brass methods

Brass::Brass(const string &s, long an, double bal)

{

    fullName=s;

    acctNum=an;

    balance=bal;

}

//储蓄函数

void Brass::Deposit(double amt)

{

    if(amt<0)

    {

        cout<<"Negative deposit not allowed;"

           <<"deposit is cancelled\n";

    }

    else

        balance=balance+amt;

}

void Brass::withdraw(double amt)

{

    //set up ###.##format

    format initialState=setFormat();

    precis prec=cout.precision(2);

    if(amt<0)

    {

        cout<<"withdrawal amouut must be positive;"

           <<"withdrawal canceled\n";

    }

    else if(amt<=balance)

    {

        balance=balance-amt;

    }

    else

    {

        cout<<"withrdrawl amout of $"<<amt

           <<" exceeds your balance\n"

          <<"withdrawal canceled\n";

    }

    restore(initialState,prec);

}

double Brass::Balance() const

{

    return balance;

}

void Brass::ViewAcct() const

{

    //set up ###.## format

    format initialState=setFormat();

    precis prec=cout.precision(2);

    cout<<"Client:"<<fullName<<endl;

    cout<<"Account Number:"<<acctNum<<endl;

    cout<<"Balance:$"<<balance<<endl;

    restore(initialState,prec);  //存储原始的格式

}

//BrassPlus的方法

BrassPlus::BrassPlus(const string &s,

                     long an, double bal,

                     double ml, double r):Brass(s,an,bal)

{

    //构造函数

    maxLoan=ml;

    owesBank=0.0;

    rate=r;

}

BrassPlus::BrassPlus(const Brass &ba, double ml, double r):Brass(ba)

{

    maxLoan=ml;

    owesBank=0.0;

    rate=r;

}

//重定义

void BrassPlus::ViewAcct() const

{

    //set up ###.##format

    format initialState=setFormat();

    precis prec=cout.precision(2);

    Brass::ViewAcct();  //显示基类的部分

    cout<<"Maximum loan:$"<<maxLoan<<endl;

    cout<<"Owed to back:$"<<owesBank<<endl;

    cout.precision(3);

    cout<<"Loan Rate"<<100*rate<<"%\n";

    restore(initialState,prec);

}

//重定义

//如果用户提取的金额超过了结余，该方法将安排贷款

void BrassPlus::withdraw(double amt)

{

    format initialState=setFormat();

    precis prec=cout.precision(2);

    //使用Balance()函数来确定结余

    double bal=Balance();

    if(amt<=bal)

    {

        //提款少于存款，提款成功

        Brass::withdraw(amt);  //继承类中调用基类的方法

    }

    else if(amt<=bal+maxLoan-owesBank)

    {

        double advance=amt-bal;

        owesBank+=advance*(1.0+rate);  //owesBank当前的透支额度

        cout<<"Bank advance:$"<<advance<<endl;

        cout<<"Finance charge:$"<<advance*rate<<endl;

        Deposit(advance);  //放贷

        //放贷成功后可以今天提款

        Brass::withdraw(amt);

    }

    else

    {

        cout<<"Credit limit exceeded.Transaction cancelled.\n";

    }

    restore(initialState,prec);

}

format setFormat()

{

    //set up ###.## format

    return cout.setf(std::ios_base::fixed,

                     std::ios_base::floatfield);

}

void restore(format f, precis p)

{

    cout.setf(f,std::ios_base::floatfield);

    cout.precision(p);

}

int main(int argc, char *argv[])

{

    cout << "Hello World!" << endl;

    using std::cout;

    using std::endl;

    Brass Piggy("Procelot Pigg",381299,4000.00);

    BrassPlus Hoggy("Horatio Hogg",382288,3000.00);

    Piggy.ViewAcct();

    cout<<endl;

    Hoggy.ViewAcct();

    cout<<"Depositing $1000 into the Hogg Account:\n";

    Hoggy.Deposit(1000.00);  //储蓄1000元到Hoggy的账户

    cout<<"New Balance:$"<<Hoggy.Balance()<<endl;

    cout<<"Withdrawing $4200 from the Pigg Account:\n";

    //取款失败，且不能借贷，因为Piggy是基类的对象，没有实现借贷的方法

    Piggy.withdraw(4200.00);

    cout<<"Pigg account balance:$"<<Piggy.Balance()<<endl;

    cout<<"Withdrwaing $42000 from the Hogg Account:\n";

    Hoggy.withdraw(4200.00);

    Hoggy.ViewAcct();

    return 0;

}

运行结果如下

IDE为Qt Creator 4.0.3 (Community)

巴特西

P493 brass

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