C++ Primer 第一章课后习题答案（附带Sales_item文件）

练习1.3

#include <iostream>

using namespace std;

int main()
{
	int s(2);
	cout << "Enter %d number" << s << std::endl;
	int v1, v2;
	cin >> v1 >> v2;
	cout << "The sum of " << v1 << " and " << v2 << " is " << v1 + v2 << std::endl;
	system("pause");
	return 0;
}

练习1.4

#include <iostream>

using namespace std;

int main()
{
	int s(2);
	cout << "Enter %d number" << s << std::endl;
	int v1, v2;
	cin >> v1 >> v2;
	cout << "The mutiply of " << v1 << " and " << v2 << " is " << v1 *v2 << std::endl;
	system("pause");
	return 0;

}

练习1.6

不合法，在分号以后本句结束，而下句没有输出流， <<会显示非法。

练习1.7

在注释中遇到意外的文件结束

练习1.8

1，2正确，3，4错误
原因：注释不可充当输出语句。

练习1.9

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

using namespace std;

int main()
{
	int s(49),sum(0);

	while (++s <= 100)
	{
		sum += s;
	}
	cout << "The sum of value added from 50 to 100 is " << sum << endl;
	system("pause");
}

练习1.10

#include <iostream>

using namespace std;

int main()
{
	int s(11);

	while (--s >= 0)
	{
		cout << " " << s << endl;
	}

	system("pause");
}

练习1.11

#include <iostream>

using namespace std;

int main()
{
	int s1(0), s2(0);
	cout << "Please input two num,and I will show you all of value between these" << endl;
	cin >> s1 >> s2;

	int i;
	/*保证s1所代表的数值为最小*/
	if (s1 >= s2)
	{
		i = s1;
		s1 = s2;
		s2 = i;
	}
	/*懒得再定义，继续复用变量，用i打印出所有数字，读者切勿学习*/
	i = s1 ;
	while (++i < s2)
	{
		cout << " " << i << endl;
	}

	system("pause");
} 

练习1.12

for循环完成了从-100到100的总和

练习1.14

在循环条件已知的情况下，我会更多的使用for循环，它清晰明了，方便维护和读懂。
如果循环条件为未知，例如循环条件为接受到某个用户命令，这种不可
知预知的条件时，我会选择while(接收到命令)。
此外，推荐一种代码写法
do
{
...
}while(0);
在过程化程序设计时，时常会遇到错误返回，但又不需要整个代码过程返回。
仅使下面的一段程序不必执行，可使用该写法。

练习1.16

#include <iostream>

using namespace std;

int main()
{
	int s1(0),sum(0);
                //旨在输入一次就出结果
	while (cin >> s1 && cin.get() != '\n')
	{
		sum += s1;
		
	}
	cout << sum << endl;
	system("pause");
}

Sales_item文件

#include <iostream>
#include <string>

#ifndef SALESITEM_H
#define SALESITEM_H

class Sales_item {
public:
	Sales_item(const std::string &book) :isbn(book), units_sold(0), revenue(0.0) {}
	Sales_item(std::istream &is) { is >> *this; }
	friend std::istream& operator>>(std::istream &, Sales_item &);
	friend std::ostream& operator<<(std::ostream &, const Sales_item &);
public:
	Sales_item & operator+=(const Sales_item&);
public:
	double avg_price() const;
	bool same_isbn(const Sales_item &rhs)const {
		return isbn == rhs.isbn;
	}
	Sales_item() :units_sold(0), revenue(0.0) {}
public:
	std::string isbn;
	unsigned units_sold;
	double revenue;
};

using std::istream;
using std::ostream;
Sales_item operator+(const Sales_item &, const Sales_item &);

inline bool operator==(const Sales_item &lhs, const Sales_item &rhs) {
	return lhs.units_sold == rhs.units_sold && lhs.revenue == rhs.revenue && lhs.same_isbn(rhs);
}

inline bool operator!=(const Sales_item &lhs, const Sales_item &rhs) {
	return !(lhs == rhs);
}

inline Sales_item & Sales_item::operator +=(const Sales_item &rhs) {
	units_sold += rhs.units_sold;
	revenue += rhs.revenue;
	return *this;
}

inline Sales_item operator+(const Sales_item &lhs, const Sales_item &rhs) {
	Sales_item ret(lhs);
	ret += rhs;
	return ret;
}

inline istream& operator>>(istream &in, Sales_item &s) {
	double price;
	in >> s.isbn >> s.units_sold >> price;
	if (in)
		s.revenue = s.units_sold * price;
	else
		s = Sales_item();
	return in;
}

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

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

练习1.20

#include <iostream>

using namespace std;

int main()
{
	Sales_item items;
	cin >> items;
	cout << items << endl;
	system("pause");
}

练习1.21

#include <iostream>

using namespace std;

int main()
{
	Sales_item items_1, items_2;
	cin >> items_1 >> items_2;

	if (items_1.isbn == items_2.isbn)
	{
		cout << items_1 + items_2 << endl;
	}
	else
	{
		cout << "Soory, The items which you input are not same" << endl;
	}
	
	system("pause");
}

练习1.22

#include <iostream>

using namespace std;

int main()
{
	Sales_item items, items_before, items_total;
	if (cin >> items_before)
	{
		items = items_before;
		items_total = items;
	}
	while (cin >> items)
	{
		if (items.isbn != items_before.isbn)
		{
			break;
		}
		items_total += items;
	}
	cout << items_total << endl;
	
	system("pause");
}

练习1.23

#include <iostream>

using namespace std;

int main()
{
	Sales_item items, items_before, items_total;
	int cnt = 0;
	if (cin >> items_before)
	{
		items = items_before;
		items_total = items;
		cnt = 1;
	}
	while (cin >> items)
	{
		if (items.isbn != items_before.isbn)
		{
			cout << items_total << '\n' << "sale cnt: " << cnt << endl;
			items_before = items;
			items_total = items;
			cnt = 1;
		}
		else
		{
			items_total += items;
			cnt += 1;
		}
	}
	
	system("pause");
}