[C++ Primer Plus] 第10章对象和类程序清单——辨析三个const

Posted 2020-10-12

程序清单10.1+10.2+10.3

头文件stock.h

#ifndef STOCK00_H_    //先测试x是否被宏定义过
#define STOCK00_H_    //如果没有宏定义,就宏定义x并编译下面的语句

#include <string>
class Stock        //类声明
{
private:
    std::string company;
    long shares;
    double share_val;
    double total_val;
    void set_tot()    {    total_val=shares*share_val;    }
public:
    void acquire(const std::string &co,long n,double pr);
    void buy(long num,double price);
    void sell(long num,double price);
    void update(double price);
    void show();
};    //千万别忘了分号

#endif    //如果已经定义了则编译#endif后面的语句

stock.cpp

#include<iostream>
#include "stock.h"

void Stock::acquire(const std::string &co,long n,double pr){
    company=co;
    if(n<0){
        std::cout<<company<<std::endl;
        shares=0;
    }else
        shares=n;
    share_val=pr;
    set_tot();
} 
    
void Stock::buy(long num,double price){
    if(num<0)
        std::cout<<"Error!\\n";
    else{
        shares+=num;
        share_val=price;
        set_tot();
    }
} 

void Stock::sell(long num,double price){
    using std::cout;
    if(num<0)
        cout<<"Error!\\n";
    else if(num>shares)
        cout<<"You can not sell more than you have!\\n";
    else{
        shares-=num;
        share_val=price;
        set_tot();
    }
}

void Stock::update(double price){
    share_val=price;
    set_tot();
}

void Stock::show(){
    std::cout<<"Company: "<<company<<", Shares:"<<shares<<"\\nShare Price: $"<<share_val<<", Total Worth: $"<<total_val<<‘\\n‘;
}

main.cpp

//用于测试Stock类的设计
#include<iostream>
#include "stock.h"

void main(){
    Stock cat;
    cat.acquire("NanoSmart",20,12.50);
    cat.show();
    cat.buy(15,18.125);
    cat.show();
    cat.sell(400,20.0);
    cat.show();
    cat.buy(300000,40.125);
    cat.show();
    cat.sell(300000,0.125);
    cat.show();
    system("pause");
}

修改stock.cpp文件中的show方法，使其数字格式统一

void Stock::show(){
    using std::cout;
    using std::ios_base;
    ios_base::fmtflags orig=cout.setf(ios_base::fixed,ios_base::floatfield);//设置cout对象的一个标记，命令cout使用定点表示法
    std::streamsize prec=cout.precision(3);//cout使用定点表示法时，显示三位小数

    cout<<"Company: "<<company<<", Shares:"<<shares<<"\\nShare Price: $"<<share_val<<", Total Worth: $"<<total_val<<‘\\n‘;
    cout.setf(orig,ios_base::floatfield);
    cout.precision(prec);
}

 

小结

 

构造函数和析构函数

程序清单10.4+10.5+10.6

头文件

#ifndef STOCK10_H_    //先测试x是否被宏定义过
#define STOCK10_H_    //如果没有宏定义,就宏定义x并编译下面的语句
#include <string>

class Stock        //类声明
{
private:
    std::string company;
    long shares;
    double share_val;
    double total_val;
    void set_tot()    {    total_val=shares*share_val;    }
public:
    Stock();    //默认构造函数
    Stock(const std::string &co,long n=0,double pr=0.0);
    ~Stock();    //析构函数
    void buy(long num,double price);
    void sell(long num,double price);
    void update(double price);
    void show();
};    //千万别忘了分号

#endif    //如果已经定义了则编译#endif后面的语句

函数定义

#include<iostream>
#include "stock.h"
using namespace std;

//构造函数
Stock::Stock(){
    cout<<"Default constructor called\\n";
    company="no name";
    shares=0;
    share_val=0.0;
    total_val=0.0;
}
Stock::Stock(const std::string &co,long n,double pr){
    cout<<"Constructor using "<<co<<" called\\n";
    company=co;
    if(n<0){
        cout<<company<<endl;
        shares=0;
    }else
        shares=n;
    share_val=pr;
    set_tot();
} 
//类的析构函数
Stock::~Stock(){
    cout<<"Bye, "<<company<<endl;
}
    
void Stock::buy(long num,double price){
    if(num<0)
        std::cout<<"Error!\\n";
    else{
        shares+=num;
        share_val=price;
        set_tot();
    }
} 

void Stock::sell(long num,double price){
    if(num<0)
        cout<<"Error!\\n";
    else if(num>shares)
        cout<<"You can not sell more than you have!\\n";
    else{
        shares-=num;
        share_val=price;
        set_tot();
    }
}

void Stock::update(double price){
    share_val=price;
    set_tot();
}

void Stock::show(){
    ios_base::fmtflags orig=cout.setf(ios_base::fixed,ios_base::floatfield);//设置cout对象的一个标记，命令cout使用定点表示法
    streamsize prec=cout.precision(3);//cout使用定点表示法时，显示三位小数
    cout<<"Company: "<<company<<", Shares:"<<shares<<"\\nShare Price: $"<<share_val;
    cout.precision(2);//显示2位小数
    cout<<", Total Worth: $"<<total_val<<endl;
    cout.setf(orig,ios_base::floatfield);
    cout.precision(prec);
}

主函数

#include<iostream>
#include "stock.h"

void main(){
    {
        using std::cout;
        cout<<"Using constructors to create new objects!!!\\n";
        Stock stock1("NanoSmart",12,20.0);
        stock1.show();
        Stock stock2=Stock ("Boffo Object",2,2.0);
        stock2.show();

        cout<<"Assigning stock1 to stock2!!!\\n";
        stock2=stock1;
        cout<<"Listing stock1 and stock2:\\n";
        stock1.show();
        stock2.show();

        cout<<"Using a constructor to reset an object!!!\\n";
        stock1=Stock("Nifty Foods",10,50.0);
        cout<<"Revised stock1:\\n";
        stock1.show();
        cout<<"Done\\n";
    }//代码执行到此处后，调用析构函数。若没有这对括号，程序将在代码退出时调用（即我们无法观察到析构函数的调用）
    system("pause");
}

最后两行输出是析构函数调用的结果。

栈先进后出

 

辨析三个const

 如声明　　const int func（const int & a） const

第一个表示返回值是个int型的常值
第二个代表const int的引用，a可读不可改
第三个代表这个函数类中的成员变量，不可修改

const Stock & topval(const Stock &s) const;//返回const Stock类型的引用：参数是引用，返回值也是引用

程序清单10.7+10.8+10.9（this）

#ifndef STOCK    
#define STOCK    
#include <string>

class Stock        //类声明
{
private:
    std::string company;
    long shares;
    double share_val;
    double total_val;
    void set_tot()    {    total_val=shares*share_val;    }
public:
    Stock();    //默认构造函数
    Stock(const std::string &co,long n=0,double pr=0.0);
    ~Stock();    //析构函数
    void buy(long num,double price);
    void sell(long num,double price);
    void update(double price);
    void show() const;    //const在后面表示不可修改函数内部的值
    const Stock & topval(const Stock &s) const;//返回const Stock类型的引用：参数是引用，返回值也是引用
};    //千万别忘了分号

#endif    

#include<iostream>
#include "stock.h"
using namespace std;

//构造函数
Stock::Stock(){
    company="no name";
    shares=0;
    share_val=0.0;
    total_val=0.0;
}
Stock::Stock(const std::string &co,long n,double pr){
    company=co;
    if(n<0){
        cout<<company<<endl;
        shares=0;
    }else
        shares=n;
    share_val=pr;
    set_tot();
} 
//类的析构函数
Stock::~Stock(){
}
    
void Stock::buy(long num,double price){
    if(num<0)
        std::cout<<"Error!\\n";
    else{
        shares+=num;
        share_val=price;
        set_tot();
    }
} 

void Stock::sell(long num,double price){
    if(num<0)
        cout<<"Error!\\n";
    else if(num>shares)
        cout<<"You can not sell more than you have!\\n";
    else{
        shares-=num;
        share_val=price;
        set_tot();
    }
}

void Stock::update(double price){
    share_val=price;
    set_tot();
}

void Stock::show() const{
    ios_base::fmtflags orig=cout.setf(ios_base::fixed,ios_base::floatfield);//设置cout对象的一个标记，命令cout使用定点表示法
    streamsize prec=cout.precision(3);//cout使用定点表示法时，显示三位小数
    cout<<"Company: "<<company<<", Shares:"<<shares<<"\\n    Share Price: $"<<share_val;
    cout.precision(2);//显示2位小数
    cout<<", Total Worth: $"<<total_val<<endl;
    cout.setf(orig,ios_base::floatfield);
    cout.precision(prec);
}

const Stock & Stock::topval(const Stock &s) const{
    if(s.total_val>total_val)
        return s;
    else 
        return *this;
} 

#include<iostream>
#include "stock.h"

const int STKS=4;
void main(){
    Stock stocks[STKS]={
        Stock("Nano",12,20.0),
        Stock("Boffo",200,2.0),
        Stock("Mono",130,3.25),
        Stock("Fleep",60,6.5),
    };
    std::cout<<"Stock holdings:\\n";
    int st;
    for (st = 0; st < STKS; st++)
        stocks[st].show();
    const Stock * top=&stocks[0];
    for (st = 1; st < STKS; st++)
        top=&top->topval(stocks[st]);
    std::cout<<"\\nMost valuale holding:\\n";
    top->show();
    system("pause");
}

程序清单10.10+10.11+10.12（栈）

#ifndef STACK    
#define STACK    

typedef unsigned long Item;

class Stack        //类声明
{
private:
    enum{MAX=10};
    Item items[MAX];
    int top;
public:
    Stack();    //默认构造函数
    bool isempty() const;
    bool isfull() const;
    bool push(const Item & item);//压栈
    bool pop(Item & item);//出栈
};    

#endif    

#include "stack.h"

//构造函数
Stack::Stack(){
    top=0;
}

bool Stack::isempty() const{
    return top==0;//top为0返回true，反之为false
}
bool Stack::isfull() const{
    return top==MAX;
}
bool Stack::push(const Item &item){
    if(top<MAX){
        items[top++]=item;
        return true;
    }else
        return false;
}
bool Stack::pop(Item &item){
    if(top>0){
        item=items[--top];
        return true;
    }else
        return false;
}

#include<iostream>
#include<cctype>
#include "stack.h"
using namespace std;

void main(){
    Stack st;
    char ch;
    unsigned long po;
    cout<<"Enter A to add a purchase order, P to process a PO, Q to quit.\\n";
    while (cin>>ch&&toupper(ch)!=‘Q‘)
    {
        while(cin.get()!=‘\\n‘)//如果不是换行就继续
            continue;
        if (!isalpha(ch))//如果不是字母就继续
        {
            cout<<‘\\a‘;
            continue;
        }
        switch (ch)
        {
        case ‘A‘:
        case ‘a‘:
            cout<<"Enter a PO number to add: ";
            cin>>po;
            if(st.isfull())//该方法判断：如果满了（top等于MAX）返回true，没满返回false
                cout<<"Stack already full\\n";
            else
                st.push(po);
            break;
        case ‘P‘:
        case ‘p‘:
            if(st.isempty())
                cout<<"Stack already empty\\n";
            else{
                st.pop(po);
                cout<<"PO #"<<po<<" popped\\n";
            }
            break;
        }
        cout<<"Enter A to add a purchase order, P to process a PO, Q to quit.\\n";
    }
    system("pause");
}