答案目录

第1章 开始

两数相加

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#include<iostream>
int main() 
{
	std::cout << "Enter two numbers:" << std::endl;
	int v1 = 0, v2 = 0;
	std::cin >> v1 >> v2;
	std::cout << "The sum of " << v1 << " and " << v2
		<< " is " << v1 + v2 << std::endl;
	return 0;
}

练习1.3

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#include<iostream>
int main() 
{
	std::cout << "Hello world" << std::endl;
	return 0;
}

练习1.4

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#include<iostream>
int main() 
{
	std::cout << "Enter two numbers:" << std::endl;
	int v1 , v2 ;
	std::cin >> v1 >> v2;
	std::cout << "The multiplication of " << v1 << " and " << v2
		<< " is " << v1 * v2 << std::endl;
	return 0;
}

练习1.5

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#include<iostream>
int main() 
{
	std::cout << "Enter two number" << std::endl;
	int a, b;
	std::cin >> a >> b;
	std::cout << "The multiplication of ";
	std::cout << a;
	std::cout << " and ";
	std::cout << b;
	std::cout << " is ";
	std::cout << a * b;
	std::cout << std::endl;
	return 0;
}

练习1.6 不合法，第一行有分号表示语句结束

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#include<iostream>
int main() 
{
	std::cout << "Input two numbers: " << std::endl;
	int v1, v2;
	std::cin >> v1 >> v2;
	std::cout << "The sum of " << v1
		<< " and " << v2
		<< " is " << v1 + v2 << std::endl;
	return 0;
}

练习1.8

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#include<iostream>
int main() 
{
	std::cout << "/*" << std::endl;
	std::cout << "*/" << std::endl;
	//std::cout << /* "*/" */<<std::endl;
	std::cout << /* "*/" /* "/*" */ << std::endl;
	return 0;
}

练习1.9

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#include<iostream>
int main() 
{
	int sum = 0, val = 50;
	while (val <= 100) {
		sum += val;
		++val;
	}
	std::cout << "Sum of 50 to 100 inclusive is "
		<< sum << std::endl;
	return 0;
}

练习1.10

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#include<iostream>
int main() 
{
	int sum = 0, val = 10;
	while (val >= 0) {
		sum += val;
		--val;
	}
	std::cout << "Sum of 0 to 10 inclusive is "
		<< sum << std::endl;
	return 0;
}

练习1.11（以下代码满足练习1.19的要求）

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#include<iostream>
int main() 
{
	int a, b, c = 0;
	std::cout << "Enter two numbers" << std::endl;
	std::cin >> a >> b;
	if (a > b) {
		c = a;
		a = b;
		b = c;
	}
	while (b >= a) {
		std::cout << a << " ";
		++a;
	}
	return 0;
}

练习1.12 程序的功能是求[-100, 100]范围内的整数的和，sum的终值为0

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#include<iostream>
int main() 
{
	int sum = 0;
	for (int i = -100; i <= 100; ++i)
		sum += i;
	std::cout << sum << std::endl;
	return 0;
}

练习1.13

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#include<iostream>
int main() 
{
	int sum = 0;
	int a, b, c = 0;
	for (int i = 50; i <= 100; ++i)
		sum += i;
	std::cout << "The sum of 50 to 100 is " << sum << std::endl;
	for (int j = 10; j >= 0; --j) {
		std::cout << j << " ";
		if (j == 0)
			std::cout << std::endl;
	}
	std::cout << "Enter two numbers" << std::endl;
	std::cin >> a >> b;
	if (a > b) {
		c = a;
		a = b;
		b = c;
	}
	for (; a <= b; ++a)
		std::cout << a << " ";
	return 0;
}

练习1.14

已知循环次数的时候用for简便，未知时用while简便

练习1.16

文件结束符（Windows系统为Ctrl+Z，然后按Enter）

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

统计值出现次数

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#include <iostream>
int main()
{
	// currVal 是我们正在统计的数;我们将读入的新值存入val
	int currVal = 0,val = 0;
	//读取第一个数，并确保确实有数据可以处理
	if (std::cin>> currVal) {
		int cnt = 1;					//保存我们正在处理的当前值的个数
		while (std::cin >> val) {		// 读取剩余的数
			if (val == currVal)			//如果值相同
				++cnt;					//将cnt加1
			else {						//否则，打印前一个值的个数
				std:: cout << currVal <<" occurs "
					<< cnt << " times" << std::endl;
				currVal = val;			//记住新值
				cnt = 1;				//重置计数器
			}
		} // while循环在这里结束
		//记住打印文件中最后一个值的个数
		std::cout << currVal << " occurs "
			<< cnt << " times" << std::endl;
	}//最外层的if语句在这里结束.
	return 0;
}

练习1.20

Sales_ item.h代码，在头文件创建该文件输入以下代码就可以用了

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#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

练习1.21

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#include <iostream>
#include "Sales_item.h"
int main(){
	Sales_item book1, book2;
	std::cin >> book1 >> book2;
	std::cout << book1 + book2 <<std::endl;
	return 0;
}