C++ Primer课后习题解答（第一章）

Preface

使用的书籍为《C++ Primer》第五版 英文版

Exercises Section 1.1

Ex1.2

Exercises Section 1.2

Ex1.3

Ex1.4

Ex1.5

Ex1.6

v1 后面多了一个冒号

Exercises Section 1.3

Ex1.7

Ex1.8

    std::cout << "/*";      // 合法
    std::cout << "*/";      // 合法
    std::cout << /* "*/" */;   // 不合法
    std::cout << /* "*/" /* "/*" */;   // 合法

不合法的更改如下：

	std::cout << /* "*/" */";

Exercises Section 1.4.1

Ex1.9

#include<iostream>

int main()
{
    int sum = 0;
    int num = 50;
    while (num <= 100)
    {
        sum = sum + num;
        num = num + 1;
    }
    std::cout << sum << std::endl;
    system("pause");
    return 0;
}

Ex1.10

#include<iostream>

int main()
{
    int num = 10;
    while (num >= 0)
    {
        std::cout << num << " ";
        num--;
    }
    std::cout << std::endl;
    system("pause");
    return 0;
}

Ex1.11

#include<iostream>

int main()
{
    int v1 = 0, v2 = 0;
    std::cout << "Enter two numbers: ";
    std::cin >> v1 >> v2;
    while (v1 <= v2)
    {
        std::cout << v1 << " ";
        v1++;
    }
    std::cout << std::endl;
    system("pause");
    return 0;
}

Exercises Section 1.4.2

Ex1.12

计算 -100 到 100 范围内所有整数的和； 最后的值为0

Ex1.13

重写了第一个，其实都是一样的

#include<iostream>

int main()
{
    int sum = 0;
    for (int i = 50; i <= 100; i++)
    {
        sum += i;
    }
    std::cout << sum << std::endl;
    system("pause");
    return 0;
}

Ex1.14

当知道循环次数时，使用 for 循环更方便；条件循环时，使用 while 循环更好。

Exercises Section 1.4.3

Ex1.16

#include<iostream>

int main()
{
    int sum = 0, value = 0;
    while (std::cin >> value)
        sum += value;
        std::cout << "Sum is: " << sum << std::endl;
    system("pause");
    return 0;
}

Exercises Section 1.4.4

Ex1.17

一个数字出现多次；多个数字，每个出现一次。

Ex1.18

Ex1.19

重写了 1.11：

#include<iostream>

int main()
{
    int v1 = 0, v2 = 0;
    std::cout << "Enter two numbers: ";
    std::cin >> v1 >> v2;
    if (v1 > v2)
    {
        int temp = v1;
        v1 = v2;
        v2 = temp;
    }
    while (v1 <= v2)
    {
        std::cout << v1 << " ";
        v1++;
    }
    std::cout << std::endl;
    system("pause");
    return 0;
}

Exercises Section 1.5.1

Ex1.20

Sales_item.h 文件如下：

#ifndef SALESITEM_H
#define SALESITEM_H
#include <iostream>
#include <string>

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

Ex1.21

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

int main()
{
	Sales_item t1, t2;
	std::cin >> t1 >> t2;
	if (t1.isbn == t2.isbn)
	{
		std::cout << t1 + t2 << std::endl;
		return 0;
	}
	else
	{
		std::cerr << "Data must refer to same ISBN" << std::endl;
		return -1;
	}
}

Ex1.22

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

int main()
{
	Sales_item total, item;
	if (std::cin >> total)
	{
		while (std::cin >> item)
		{
			if (item.isbn == total.isbn)
			{
				total += item;
			}
			else
			{
				std::cout << total << std::endl;
				total = item;
			}
		}
		std::cout << total << std::endl;
	}
	else
	{
		std::cerr << "No data !" << std::endl;
		return -1;
	}
    return 0;
}

Ex1.23

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

int main()
{
	Sales_item total, item;
	if (std::cin >> total)
	{
		int cnt = 1;
		while (std::cin >> item)
		{
			if (item.isbn == total.isbn)
			{
				cnt++;
			}
			else
			{
				std::cout << total.isbn << " " << cnt << std::endl;
				total = item;
			}
		}
		std::cout << total.isbn << " " << cnt << std::endl;
	}
	else
	{
		std::cerr << "No data !" << std::endl;
		return -1;
	}
	return 0;
}