(2011.07.14) 类的基本应用实例。

// stocks.cpp -- the whole program
#include <iostream>
#include <cstring>

class Stock // class declaration
{
	private:
		char company[30];
		int shares;
		double share_val;
		double total_val;
		void set_tot(){ total_val = shares * share_val;}
	public:
		void acquire(const char* co, int n, double pr);
		void buy(int num, double price);
		void sell(int num, double price);
		void update(double price);
		void show();
};			// note semicolon at the end

void Stock::acquire(const char* co, int n, double pr)
{
	std::strncpy(company, co, 29);	// truncate co to fit company
	company[29] = '\0';
	if (n < 0)
	{
		std::cerr << "Number of shares can't be negative."
					<< company << " shares set to 0. \n";
		shares = 0;
	}
	else
		shares = n;
	share_val = pr;
	set_tot();
}

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

}

void Stock::sell(int num, double price)
{
	using std::cerr;
	if (num < 0)
	{
		cerr << "Number of shares sold can't be negative. "
				<< "Transaction is aborted.\n";
	}
	else if (num > shares)
	{
		cerr << "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()
{
	using std::cout;
	using std::endl;
	cout << "Company: " << company
		<< " Shares: " << shares << endl
		<< " Share Price: {1}quot; << share_val
		<< " Total Worth: {1}quot; << total_val << endl;
}

int main()
{
	using std::cout;
	using std::ios_base;
	Stock stock1;
	stock1.acquire("NanoSmart", 20, 12.50);
	cout.setf(ios_base::fixed);
	cout.precision(2);
	cout.setf(ios_base::showpoint);
	stock1.show();
	stock1.buy(15, 18.25);
	stock1.show();
	stock1.sell(400, 20.00);
	stock1.show();
	return 0;
}