C++|C++ primer第一章小结

        本章学习了如何定义main函数，以及定义基本变量，如何进行输入输出，以及常见的条件语句结果和循环结构。

        以一个书店小程序结尾，可以统计连续出现的数据的次数。

Sales_item.h

#ifndef SALESITEM_H
// we're here only if SALESITEM_H has not yet been defined 
#define SALESITEM_H

// Definition of Sales_item class and related functions goes here
#include 
#include 

class Sales_item {
	// these declarations are explained section 7.2.1, p. 270 
	// and in chapter 14, pages 557, 558, 561
	friend std::istream& operator>>(std::istream&, Sales_item&);
	friend std::ostream& operator<<(std::ostream&, const Sales_item&);
	friend bool operator<(const Sales_item&, const Sales_item&);
	friend bool
		operator==(const Sales_item&, const Sales_item&);
public:
	// constructors are explained in section 7.1.4, pages 262 - 265
	// default constructor needed to initialize members of built-in type
	Sales_item() : units_sold(0), revenue(0.0) { }
	Sales_item(const std::string &book) :
		bookNo(book), units_sold(0), revenue(0.0) { }
	Sales_item(std::istream &is) { is >> *this; }
public:
	// operations on Sales_item objects
	// member binary operator: left-hand operand bound to implicit this pointer
	Sales_item& operator+=(const Sales_item&);

	// operations on Sales_item objects
	std::string isbn() const { return bookNo; }
	double avg_price() const;
	// private members as before
private:
	std::string bookNo;      // implicitly initialized to the empty string
	unsigned units_sold;
	double revenue;
};

// used in chapter 10
inline
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)
{
	return lhs.isbn() == rhs.isbn();
}

// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);

inline bool
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
	// must be made a friend of Sales_item
	return lhs.units_sold == rhs.units_sold &&
		lhs.revenue == rhs.revenue &&
		lhs.isbn() == rhs.isbn();
}

inline bool
operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
	return !(lhs == rhs); // != defined in terms of operator==
}

// assumes that both objects refer to the same ISBN
Sales_item& Sales_item::operator+=(const Sales_item& rhs)
{
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;
	return *this;
}

// assumes that both objects refer to the same ISBN
Sales_item
operator+(const Sales_item& lhs, const Sales_item& rhs)
{
	Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return
	ret += rhs;           // add in the contents of (|rhs|) 
	return ret;           // return (|ret|) by value
}

std::istream&
operator>>(std::istream& in, Sales_item& s)
{
	double price;
	in >> s.bookNo >> s.units_sold >> price;
	// check that the inputs succeeded
	if (in)
		s.revenue = s.units_sold * price;
	else
		s = Sales_item();  // input failed: reset object to default state
	return in;
}

std::ostream&
operator<<(std::ostream& out, const Sales_item& s)
{
	out << s.isbn() << " " << s.units_sold << " "
		<< s.revenue << " " << s.avg_price();
	return out;
}

double Sales_item::avg_price() const
{
	if (units_sold)
		return revenue / units_sold;
	else
		return 0;
}
#endif

书店小程序.cpp

#include
#include"Sales_item.h"
using namespace std;

统计输入中每个值的出现次数
//void test01()
//{
//	//currVal是正在统计的数，val用于存读入的新值
//	int currVal = 0, val = 0;
//	if (cin >> currVal)
//	{
//		int cnt = 1;//保存正在处理的当前值的个数
//		while (cin >> val)//读取剩余的数
//		{
//			if (val == currVal)//如果值相同
//			{
//				++cnt;
//			}
//			else
//			{
//				cout << currVal << " 出现了 " << cnt << " 次" << endl;
//				currVal = val;
//				cnt = 1;
//
//			}
//		}
//		cout << currVal << " 出现了 " << cnt << " 次" << endl;
//		
//	}
//
//}

void test01()
{
	
	//读取多条销售记录，并统计每个ISBN有几条销售记录
	Sales_item currItem,item;
	if (cin >> currItem)
	{
		int cnt = 1;
		while (cin >> item)
		{
			if (currItem.isbn() == item.isbn())//ISBN相同
			{
				cnt++;
			}
			else//ISBN不同
			{
				cout << currItem.isbn() << "有" << cnt << "条销售记录" << endl;
				currItem = item;
				cnt = 1;
			}
			cout << currItem.isbn() << "有" << cnt << "条销售记录" << endl;
		}
		
	}
		
}


void test02()
{
	//保存下一条交易记录的变量
	Sales_item total;
	//读入第一条交易记录，确保有数据可以处理
	if (cin >> total)
	{
		Sales_item trans;
		while (cin >> trans)
		{
			//如果仍在处理相同的书
			if (total.isbn() == trans.isbn())
			{
				//更新总销售额
				total += trans;
			}
			else
			{
				//打印前一本书的结果
				cout << total << endl;
				//total现在表示下一本书的销售额
				total = trans;
			}
		}
		//打印最后一本书的结果
		cout << total << endl;
	}
	else
	{
		//没有输入
		cout << "没有数据输入" << endl;

	}
}
int main()
{
	
	test02();

	system("pause");
	return 0;
}