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类和继承(c++primer plus 学习笔记13章)

作者:互联网

1.派生类和基类是一种is-a的关系,即派生类对象也是一个基类对象,可以对基类对象执行任何操作。

2.多态:同一个方法(c++中称为函数)在派生类和基类中的行为方式是不同的,换句话说就是方法的行为处决于调用该方法的对象。例如一个称为clean的方法,有的类执行扫地,有的类执行擦窗,有的类执行倒垃圾......但都是调用这个clean的方法。

两个重要的机制可以实现多态

(1).在派生类中重新定义基类的方法。

(2).使用虚方法。如果是通过引用或指针调用,程序将根据引用或指针指向的对象类型来选择方法。

3.派生类构造函数在初始化基类私有数据时,采用的是成员初始化列表语法

BrassPlus::BrassPlus(const std::string &s, long an, double bal, double ml, double r):Brass(s,an,bal)

brass 源码

1.brass.h 头文件

#ifndef BRASS_H
#define BRASS_H
#include<string>
 
class Brass
{
private:
    std::string fullName;
    long acctNum;
    double balance;
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);//取现,取回存款
    double Balance()const;//余额
    virtual void ViewAcct()const;//显示账号
    virtual ~Brass(){}
};
 
#endif // BRASS_H

1.brass.h 源文件

#include "brass.h"
#include<iostream>
using namespace std;
//确定小数格式及精度
typedef std::ios_base::fmtflags format;
typedef std::streamsize precis;
format setFormat();
void restore(format f,precis p);
Brass::Brass(const std::string &s, long an, double bal)
{
  fullName=s;
  acctNum=an;
  balance=bal;
}
//存款
void Brass::Deposit(double amt)
{
  if(amt<0)
      cout<<"Negative deposit not allowed; "
         <<"deposit is cancelled.\n";
  else
      balance +=amt;
}
//取款
void Brass::Withdraw(double amt)
{
   format initialState = setFormat();
   precis prec=cout.precision(2); //precision 准确
   //positive 正数
   if (amt<0)
       cout<<"Withdrawal amout must be positive;"
          <<"withdrawal canceled.\n";
   else if (amt<=balance)//取款数小于余额
       balance-=amt;
   else
       cout<<"Withdrawal amout of $"<<amt
          <<"exceeds your balance.\n"
         <<"withdrawal canceled.\n";
           restore(initialState,prec);
}
 
double Brass::Balance() const
{
  return balance;
 
}
 
void Brass::ViewAcct() const
{
    format initialState = setFormat();
        precis prec = cout.precision(2);
        cout << "Client: " << fullName << endl;
        cout << "Account Number: " << acctNum << endl;
        cout << "Balance: $" << balance << endl;
        restore(initialState, prec); // Restore original format
}
format setFormat()
{
    // set up ###.## format 设置显示格式
    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);//精度
}

brassplus 头文件

#ifndef BRASSPLUS_H
#define BRASSPLUS_H
#include"brass.h"
#include<iostream>
using namespace std;
class BrassPlus : public Brass
{
private:
    double maxLoan;
    double rate;
    double owesBank;
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 // BRASSPLUS_H
brassplus 源文件
#include "brassplus.h"
#include"brass.h"
typedef std::ios_base::fmtflags format;
typedef std::streamsize precis;
format setFormat();
void restore(format f, precis p);
BrassPlus::BrassPlus(const std::string &s, long an, double bal, double ml, double r):Brass(s,an,bal)
{
    maxLoan = ml;//最大贷款额度
        owesBank = 0.0;
        rate = r;//利率
}
//用于隐含拷贝构造函数
BrassPlus::BrassPlus(const Brass &ba, double ml, double r):Brass(ba)
{
    maxLoan = ml;
        owesBank = 0.0;
        rate = r;
}
//重新定义 显示账号的信息
void BrassPlus::ViewAcct() const
{
    format initialState = setFormat();
        precis prec = cout.precision(2);
 
        Brass::ViewAcct();   // display base portion  如果没写Brass::制定域将会无穷递归调用
        cout << "Maximum loan: $" << maxLoan << endl;
        cout << "Owed to bank: $" << owesBank << endl;
        cout.precision(3);  // ###.### format
        cout << "Loan Rate: " << 100 * rate << "%\n";
        restore(initialState, prec);
}
 
void BrassPlus::Withdraw(double amt)
{
    format initialState = setFormat();
        precis prec = cout.precision(2);
       //需通过基类公有访问基类的私有变量 获取余额
        double bal = Balance();
        if (amt <= bal)
            Brass::Withdraw(amt);
        else if ( amt <= bal + maxLoan - owesBank)//存款+最大信用额度-欠款
        {
            double advance = amt - bal;
            owesBank += advance * (1.0 + rate);
            cout << "Bank advance: $" << advance << endl;
            cout << "Finance charge: $" << advance * rate << endl;
            Deposit(advance);
            Brass::Withdraw(amt);
        }
        else
            cout << "Credit limit exceeded. Transaction cancelled.\n";//Credit贷款
        restore(initialState, prec);
}
 

标签:13,cout,format,double,void,c++,plus,Brass,amt
来源: https://blog.csdn.net/delphi863/article/details/118079476