程序清单10.7，10.8，10.9-课本298，299，301页

stock20.h

#ifndef STOCK20_H_
#define STOCK20_H_
#include<string>

class Stock
{
private:
std::string company;
int shares;
double share_val;
double total_val;
void set_tot()
{
total_val=shares* share_val;
}
public:
Stock();
Stock(const std::string & co,long n=0,double pr=0.0);
~Stock();
void buy(long num,double price);
void sell(long num,double price);
void update(double price);
void show() const;
const Stock & topval(const Stock & s) const;
};
#endif

stock20.cpp

#include<iostream>
#include"stock20.h"

Stock::Stock()
{
company="no time";
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)
{
std::cout<<"Number of shares can't be negative; "
<<company<<" shares set to 0.\n";
shares=0;
}
else
shares=n;
share_val=pr;
set_tot();
}

Stock::~Stock()
{
}

void Stock::buy(long num,double price)
{
if (num<0)
{
std::cout<<"Number of shares purchased can't be negative. "
<<"Transaction is aborted.\n";
}
else
{
shares+=num;
share_val=price;
set_tot();
}
}

void Stock::sell(long num,double price)
{
using std::cout;
if (num<0)
{
cout<<"NUmber of shares sold can't be negative."
<<"Transaction is aborted.\n";
}
else if (num>shares)
{
cout<<"You can't sell more than you have! "
<<"Transaction is aborted.\n";
}
else
{
shares-=num;
share_val=price;
set_tot();
}
}

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

void Stock::show() const
{
using std::cout;
using std::ios_base;

ios_base::fmtflags orig=cout.setf(ios_base::fixed,ios_base::floatfield);
std::streamsize prec=cout.precision(3);

cout<<"Company："<<company
<<" Shares："<<shares<<'\n';
cout<<" Share Price：$"<<share_val;

cout.precision(2);
cout<<" Total Worth：$"<<total_val<<'\n';

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;
}

usestock2.cpp

 

#include<iostream>
#include"stock20.h"

 

const int STKS=4;
int main()
{
Stock stocks[STKS]=
{
Stock("NanoSmart",12,20.0),
Stock("Boffo Objects",200,2.0),
Stock("Monolithic Obelisks",130,3.25),
Stock("Fleep Enterprises",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 valuable holding:\n";
top->show();
system("pause");
return 0;
}