C++Primer第五版 ——— （ch1）课后习题参考答案
练习 1.3
编写程序，在标准输出上打印Hello, World。
#include <iostream>
using namespace std;
int main()
{
char arr[10] = { 0 };
char arr0[10] = { 0 };
char arr1[] = "hello, world";
cin >> arr;
cin >> arr0;
cout << arr << " " << arr0 << endl;
cout << arr1 << endl;
return 0;
}
练习 1.4
我们的程序使用加法运算符+来将两个数相加。编写程序使用惩罚运算符*，来打印两个数的积。
#include <iostream>
using namespace std;
int main()
{
int a = 0, b = 0;
cout << "please enter two number:";
cin >> a >> b;
cout << "the sum of " << a << " and " << b << " is " << a + b << endl;
cout << "the multiply of " << a << " and " << b << " is " << a * b << endl;
return 0;
}
练习1.5
我们将所有输出放在一条很长的语句中。重写程序，将每个运算对象的打印操作放在一条独立的语句中。
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 0;
cout << "please enter two number:";
cin >> a;
cin >> b;
cout << "the sum of ";
cout << a;
cout << " and ";
cout << b;
cout << " is ";
cout << a + b;
cout << endl;
cout << "the multiply of ";
cout << a;
cout << " and ";
cout << b;
cout << " is ";
cout << a * b;
cout << endl;
return 0;
}
练习1.6
解释下面的程序片段是否合法。
std::cout << "The sum of " << v1;
<< "and " << v2;
<< " is " << v1+v2 << std::endl;
不合法。前两行的末尾有分号，代表语句结束，第2、3两行为两条新的语句。而这两条语句在“<<”之前缺少了输出流，应在“<<”之前加上"cout"。
改为：
练习1.7
编译一个包含不正确的嵌套注释的程序，观察编译器返回的错误信息。
#include <iostream>
/*
* 注释对/* */不能嵌套
* “不能嵌套”几个字会被认为是源码，像剩余程序一样处理
*/
int main (void)
{
return 0;
}
练习1.8
指出下列哪些输出语句是合法的（如果有的话）。
std::cout << "/*";
std::cout << "*/";
std::cout << /* "*/" */;
std::cout << /* "*/" /* "/*" */;
预测编译这些语句会产生什么样的结果，实际编译这些语句来验证你的答案（编写一个小程序，每次将上述一条语句作为其主体），改正每个编译错误。
第一条和第二条语句是合法的，第三条语句的第一个双引号和第四个双引号左引号被注释掉了，第二个双引号和第三个双引号之间的“*/”被认为是字符串的文字内容。
练习1.9
编写程序，使用while循环将50到100的整数相加。
#include <iostream>
using namespace std;
int main()
{
int a = 50;
int cut = 0;
while (a <= 100)
{
cut += a;
++a;
}
cout << "sum is " << cut << endl;
return 0;
}
练习1.10
除了++运算符将运算对象的值增加1以外，还有一个递减运算符（–）实现将值减少1。编写程序，使用递减运算符在循环中按递减序打印出10到0之间的整数。
#include <iostream>
using namespace std;
void main()
{
int i=10;
while (i >= 0)
{
cout << i << endl;
--i;
}
}
练习1.11
编写程序，提示用户输入两个整数，打印出这两个整数所指定的范围内的所有整数。
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 0;
cout << "输入两个整数：";
cin >> a >> b;
if (a > b)
{
int t = 0;
t = a;
a = b;
b = t;
}
while (a <= b)
{
cout << a << " ";
++a;
}
return 0;
}
练习1.12
下面的for循环完成了什么功能？sum的终值是多少？
int sum = 0;
for (int i = -100; i <= 100; ++i)
sum += i;
-100到100之间（包含-100和100）的整数相加，sum的终值为0。
练习1.14
对比for循环和while循环，两种形式的优缺点各是什么？
循环次数已知的情况下，for循环更为简洁；无法预知循环次数是，while循环更合适。
练习1.16
编写程序，从cin读取一组数，输出其和。
练习1.18
编译并运行本节的程序，给它输入全都相等的值。再次运行程序，输入没有重复的值。
#include <iostream>
using namespace std;
int main()
{
int a = 0;
int b = 0;
if (cin >> a)
{
int cut = 1;
while (cin >> b)
{
if (a == b)
{
++cut;
}
else
{
cout << a << "连续重复个数为：" << cut << "个" << endl;
cut = 0;
a = b;
}
}
cout << a << "连续重复个数为：" << cut << "个" << endl;
}
return 0;
}
练习1.20
在网站http://www.informit.com/title/0321714113上，第1章的代码目录汇总包含了头文件Sales_item.h。将它拷贝到你自己的工作目录中。用它编写一个程序，读取一组书籍销售记录，将每条记录打印到标准输出上。
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 <iostream>
#include <string>
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() = default;
Sales_item(const std::string &book): bookNo(book) { }
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 = 0; // explicitly initialized
double revenue = 0.0;
};
// 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
#include <iostream>
#include "Sales_item.h"
using namespace std;
int main (void)
{
Sales_item book;
cout << "请输入销售记录：" << endl;
while (cin >> book)
cout << "ISBN、销售额和平均售价为 " << book << endl;
return 0;
}
