C++ primer plus(第六版)编程练习答案第9章内存空间和名称空间

太过爱你忘了你带给我的痛 2024-03-24 08:34 9阅读 0赞

## 一、程序清单 ##

## coordin.h ##

// coordin.h -- structure templates and function prototypes
    // structure templates
    #ifndef COORDIN_H_
    #define COORDIN_H_
    
    struct polar
    {
    	double distance;    // distance from origin
    	double angle;        // direction from origin
    };
    struct rect
    {
    	double x;        // horizontal distance from origin
    	double y;        // vertical distance from origin
    };
    
    // prototypes
    polar rect_to_polar(rect xypos);
    void show_polar(polar dapos);
    
    #endif

## file1.cpp ##

// file1.cpp -- example of a three-file program
    #include <iostream>
    #include "coordin.h" // structure templates, function prototypes
    using namespace std;
    int main()
    {
        rect rplace;
        polar pplace;
    
        cout << "Enter the x and y values: ";
        while (cin >> rplace.x >> rplace.y)  // slick use of cin
        {
            pplace = rect_to_polar(rplace);
            show_polar(pplace);
            cout << "Next two numbers (q to quit): ";
        }
        cout << "Bye!\n";
    // keep window open in MSVC++
    /*
        cin.clear();
        while (cin.get() != '\n')
            continue;
        cin.get();
    */
        return 0; 
    }

## file2.cpp ##

// file2.cpp -- contains functions called in file1.cpp
    #include <iostream>
    #include <cmath>
    #include "coordin.h" // structure templates, function prototypes
    
    // convert rectangular to polar coordinates
    polar rect_to_polar(rect xypos)
    {
    	using namespace std;
    	polar answer;
    
    	answer.distance =
    		sqrt(xypos.x * xypos.x + xypos.y * xypos.y);
    	answer.angle = atan2(xypos.y, xypos.x);
    	return answer;      // returns a polar structure
    }
    
    // show polar coordinates, converting angle to degrees
    void show_polar(polar dapos)
    {
    	using namespace std;
    	const double Rad_to_deg = 57.29577951;
    
    	cout << "distance = " << dapos.distance;
    	cout << ", angle = " << dapos.angle * Rad_to_deg;
    	cout << " degrees\n";
    }

执行结果：

Enter the x and y values: 120 80
    distance = 144.222, angle = 33.6901 degrees
    Next two numbers (q to quit): 120 50
    distance = 130, angle = 22.6199 degrees
    Next two numbers (q to quit): q
    Bye!

## autoscp.cpp ##

// autoscp.cpp -- illustrating scope of automatic variables
    #include <iostream>
    void oil(int x);
    int main()
    {
    	using namespace std;
    
    	int texas = 31;
    	int year = 2011;
    	cout << "In main(), texas = " << texas << ", &texas = ";
    	cout << &texas << endl;
    	cout << "In main(), year = " << year << ", &year = ";
    	cout << &year << endl;
    	oil(texas);//5 31 113 31
    	cout << "In main(), texas = " << texas << ", &texas = ";
    	cout << &texas << endl;
    	cout << "In main(), year = " << year << ", &year = ";
    	cout << &year << endl;
    	// cin.get();
    	return 0;
    }
    
    void oil(int x)
    {
    	using namespace std;
    	int texas = 5;
    
    	cout << "In oil(), texas = " << texas << ", &texas = ";
    	cout << &texas << endl;
    	cout << "In oil(), x = " << x << ", &x = ";
    	cout << &x << endl;
    	{                               // start a block
    		int texas = 113;
    		cout << "In block, texas = " << texas;
    		cout << ", &texas = " << &texas << endl;
    		cout << "In block, x = " << x << ", &x = ";//31
    		cout << &x << endl;
    	}                               // end a block
    	cout << "Post-block texas = " << texas;//5
    	cout << ", &texas = " << &texas << endl;
    }

执行结果：

In main(), texas = 31, &texas = 00FCF764
    In main(), year = 2011, &year = 00FCF758
    In oil(), texas = 5, &texas = 00FCF670
    In oil(), x = 31, &x = 00FCF684
    In block, texas = 113, &texas = 00FCF664
    In block, x = 31, &x = 00FCF684
    Post-block texas = 5, &texas = 00FCF670
    In main(), texas = 31, &texas = 00FCF764
    In main(), year = 2011, &year = 00FCF758

## external.cpp ##

// external.cpp -- external variable
    // compile with support.cpp
    #include <iostream>
    // external variable
    double warming = 0.3;       // warming defined
    
    // function prototypes
    void update(double dt);
    void local();
    
    int main()                  // uses global variable
    {
    	using namespace std;
    	cout << "Global warming is " << warming << " degrees.\n";
    	update(0.1);            // call function to change warming
    	cout << "Global warming is " << warming << " degrees.\n";
    	local();                // call function with local warming
    	cout << "Global warming is " << warming << " degrees.\n";
    	// cin.get();
    	return 0;
    }

## support.cpp ##

// support.cpp -- use external variable
    // compile with external.cpp
    #include <iostream>
    extern double warming;  // use warming from another file
    
    // function prototypes
    void update(double dt);
    void local();
    
    using std::cout;
    void update(double dt)      // modifies global variable
    {
    	extern double warming;  // optional redeclaration
    	warming += dt;          // uses global warming
    	cout << "Updating global warming to " << warming;
    	cout << " degrees.\n";
    }
    
    void local()                // uses local variable
    {
    	double warming = 0.8;   // new variable hides external one
    
    	cout << "Local warming = " << warming << " degrees.\n";
    	// Access global variable with the
    	// scope resolution operator
    	cout << "But global warming = " << ::warming;
    	cout << " degrees.\n";
    }

执行结果：

Global warming is 0.3 degrees.
    Updating global warming to 0.4 degrees.
    Global warming is 0.4 degrees.
    Local warming = 0.8 degrees.
    But global warming = 0.4 degrees.
    Global warming is 0.4 degrees.

## twofile1.cpp ##

// twofile1.cpp -- variables with external and internal linkage
    #include <iostream>     // to be compiled with two file2.cpp
    int tom = 3;            // external variable definition
    int dick = 30;          // external variable definition
    static int harry = 300; // static, internal linkage
    // function prototype
    void remote_access();
    
    int main()
    {
    	using namespace std;
    	cout << "main() reports the following addresses:\n";
    	cout << &tom << " = &tom, " << &dick << " = &dick, ";
    	cout << &harry << " = &harry\n";
    	remote_access();
    	// cin.get();
    	return 0;
    }

## twofile2.cpp ##

// twofile2.cpp -- variables with internal and external linkage
    #include <iostream>
    extern int tom;         // tom defined elsewhere
    static int dick = 10;   // overrides external dick
    int harry = 200;        // external variable definition,
    						// no conflict with twofile1 harry
    
    void remote_access()
    {
    	using namespace std;
    
    	cout << "remote_access() reports the following addresses:\n";
    	cout << &tom << " = &tom, " << &dick << " = &dick, ";
    	cout << &harry << " = &harry\n";
    }

执行结果：

> **（两个文件使用了同样一个tom变量，但使用了不同的dick和harry变量）**
> 
> **两个tom变量的地址将相同，而两个dick和harry变量的地址不同。**

main() reports the following addresses:
    0072C000 = &tom, 0072C004 = &dick, 0072C008 = &harry
    remote_access() reports the following addresses:
    0072C000 = &tom, 0072C014 = &dick, 0072C010 = &harry

## static.cpp ##

// static.cpp -- using a static local variable
    #include <iostream>
    // constants
    const int ArSize = 10;
    
    // function prototype
    void strcount(const char * str);
    
    int main()
    {
    	using namespace std;
    	char input[ArSize];
    	char next;
    
    	cout << "Enter a line:\n";
    	cin.get(input, ArSize);
    	while (cin)
    	{
    		cin.get(next);
    		while (next != '\n')    // string didn't fit!
    			cin.get(next);      // dispose of remainder
    		strcount(input);
    		cout << "Enter next line (empty line to quit):\n";
    		cin.get(input, ArSize);
    	}
    	cout << "Bye\n";
    	// code to keep window open for MSVC++
    	/*
    	cin.clear();
    		while (cin.get() != '\n')
    			continue;
    		cin.get();
    	*/
    	return 0;
    }
    
    void strcount(const char * str)
    {
    	using namespace std;
    	static int total = 0;        // static local variable
    	int count = 0;               // automatic local variable
    
    	cout << "\"" << str << "\" contains ";
    	while (*str++)               // go to end of string
    		count++;
    	total += count;
    	cout << count << " characters\n";
    	cout << total << " characters total\n";//静态变量total只是在程序运行时被设置为0
    	//以后在两次函数调用之间，其值将保持不变，所以能够记录读取的字符总数
    }

执行结果：

Enter a line:
    nice pants
    "nice pant" contains 9 characters
    9 characters total
    Enter next line (empty line to quit):
    thanks
    "thanks" contains 6 characters
    15 characters total
    Enter next line (empty line to quit):
    parting is such sweet sorrow
    "parting i" contains 9 characters
    24 characters total
    Enter next line (empty line to quit):
    ok
    "ok" contains 2 characters
    26 characters total
    Enter next line (empty line to quit):
    
    Bye

## newplace.cpp ##

// newplace.cpp -- using placement new
    #include <iostream>
    #include <new> // for placement new
    const int BUF = 512;
    const int N = 5;
    char buffer[BUF];      // chunk of memory
    int main()
    {
    	using namespace std;
    
    	double *pd1, *pd2;
    	int i;
    	cout << "Calling new and placement new:\n";
    	pd1 = new double[N];           // use heap
    	pd2 = new (buffer) double[N];  // use buffer array
    	for (i = 0; i < N; i++)
    		pd2[i] = pd1[i] = 1000 + 20.0 * i;
    	cout << "Memory addresses:\n" << "  heap: " << pd1
    		<< "  static: " << (void *)buffer << endl;
    	cout << "Memory contents:\n";
    	for (i = 0; i < N; i++)
    	{
    		cout << pd1[i] << " at " << &pd1[i] << "; ";
    		cout << pd2[i] << " at " << &pd2[i] << endl;
    	}
    
    	cout << "\nCalling new and placement new a second time:\n";
    	double *pd3, *pd4;
    	pd3 = new double[N];            // find new address
    	pd4 = new (buffer) double[N];  // overwrite old data
    	for (i = 0; i < N; i++)
    		pd4[i] = pd3[i] = 1000 + 40.0 * i;
    	cout << "Memory contents:\n";
    	for (i = 0; i < N; i++)
    	{
    		cout << pd3[i] << " at " << &pd3[i] << "; ";
    		cout << pd4[i] << " at " << &pd4[i] << endl;
    	}
    
    	cout << "\nCalling new and placement new a third time:\n";
    	delete[] pd1;
    	pd1 = new double[N];
    	pd2 = new (buffer + N * sizeof(double)) double[N];
    	for (i = 0; i < N; i++)
    		pd2[i] = pd1[i] = 1000 + 60.0 * i;
    	cout << "Memory contents:\n";
    	for (i = 0; i < N; i++)
    	{
    		cout << pd1[i] << " at " << &pd1[i] << "; ";
    		cout << pd2[i] << " at " << &pd2[i] << endl;
    	}
    	delete[] pd1;
    	delete[] pd3;
    	// cin.get();
    	return 0;
    }

执行结果：

Calling new and placement new:
    Memory addresses:
      heap: 010C9518  static: 00A5D2D8
    Memory contents:
    1000 at 010C9518; 1000 at 00A5D2D8
    1020 at 010C9520; 1020 at 00A5D2E0
    1040 at 010C9528; 1040 at 00A5D2E8
    1060 at 010C9530; 1060 at 00A5D2F0
    1080 at 010C9538; 1080 at 00A5D2F8
    
    Calling new and placement new a second time:
    Memory contents:
    1000 at 010C9228; 1000 at 00A5D2D8
    1040 at 010C9230; 1040 at 00A5D2E0
    1080 at 010C9238; 1080 at 00A5D2E8
    1120 at 010C9240; 1120 at 00A5D2F0
    1160 at 010C9248; 1160 at 00A5D2F8
    
    Calling new and placement new a third time:
    Memory contents:
    1000 at 010C9518; 1000 at 00A5D300
    1060 at 010C9520; 1060 at 00A5D308
    1120 at 010C9528; 1120 at 00A5D310
    1180 at 010C9530; 1180 at 00A5D318
    1240 at 010C9538; 1240 at 00A5D320

## namesp.h ##

// namesp.h
    #include <string>
    // create the pers and debts namespaces
    namespace pers
    {
        struct Person
        { 
            std::string fname;
            std::string lname;
         };
        void getPerson(Person &);
        void showPerson(const Person &);
    }
    
    namespace debts
    {
        using namespace pers;
        struct Debt
        {
            Person name;
            double amount;
        };
        
        void getDebt(Debt &);
        void showDebt(const Debt &);
        double sumDebts(const Debt ar[], int n); 
    }

## namesp.cpp ##

// namesp.cpp -- namespaces
    #include <iostream>
    #include "namesp.h"
    
    namespace pers
    {
        using std::cout;
        using std::cin;
        void getPerson(Person & rp)
        {
            cout << "Enter first name: ";
            cin >> rp.fname;
            cout << "Enter last name: ";
            cin >> rp.lname;
        }
        
        void showPerson(const Person & rp)
        {
            std::cout << rp.lname << ", " << rp.fname;
        }
    }
    
    namespace debts
    {
        void getDebt(Debt & rd)
        {
            getPerson(rd.name);
            std::cout << "Enter debt: ";
            std::cin >> rd.amount;
        }
        
        void showDebt(const Debt & rd)
        {
            showPerson(rd.name);
            std::cout <<": $" << rd.amount << std::endl;
        }
        
        double sumDebts(const Debt ar[], int n)
        {
            double total = 0;
            for (int i = 0; i < n; i++)
                total += ar[i].amount;
            return total;
        }
    }

## usenmsp.cpp ##

// usenmsp.cpp -- using namespaces
    #include <iostream>
    #include "namesp.h"
    
    void other(void);
    void another(void);
    int main(void)
    {
        using debts::Debt;
    	using debts::showDebt;
        Debt golf = { {"Benny", "Goatsniff"}, 120.0 };
        showDebt(golf);
        other();
        another(); 
    	// std::cin.get();
    	// std::cin.get();
        return 0;
    }
    
    void other(void)
    {
        using std::cout;
        using std::endl;
        using namespace debts;
        Person dg = {"Doodles", "Glister"};
        showPerson(dg);
        cout << endl;
        Debt zippy[3];
        int i;
        
        for (i = 0; i < 3; i++)
            getDebt(zippy[i]);
    
        for (i = 0; i < 3; i++)
            showDebt(zippy[i]);
        cout << "Total debt: $" << sumDebts(zippy, 3) << endl;
        
        return;
    }
    
    void another(void)
    {
        using pers::Person;;
        
        Person collector = { "Milo", "Rightshift" };
        pers::showPerson(collector);
        std::cout << std::endl; 
    }

执行结果：

**（选中3个执行文件进行编译）**

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA6ZW_5rKZ5pyJ6IKl6bG8_size_20_color_FFFFFF_t_70_g_se_x_16][]

Goatsniff, Benny: $120
    Glister, Doodles
    Enter first name: Arabella
    Enter last name: Binx
    Enter debt: 100
    Enter first name: Cleve
    Enter last name: Delaproux
    Enter debt: 120
    Enter first name: Eddie
    Enter last name: Fiotox
    Enter debt: 200
    Binx, Arabella: $100
    Delaproux, Cleve: $120
    Fiotox, Eddie: $200
    Total debt: $420
    Rightshift, Milo

## 二、复习题 ##

1. 对于下面的情况，应使用哪种存储方案？

*  **a. homer是函数的形参。**
 *  **b. secret变量由两个文件共享。**
 *  **c. topsecret变量由一个文件中的所有函数共享，但对于其他文件来说是隐蔽的。**
 *  **d. beencalled记录包含它的函数被调用的次数**

a. home将自动成为自动变量。

b. secret在一个文件应该定义为一个外部变量，在第二个文件用extern声明。

c. 在topsecret前面添加关键字static，将topsecret定义为一个有内部链接的静态变量。或者将其在一个未命名的的名称空间中进行定义。

d. 在beencalled前面添加关键字static，将其定义为一个本地静态变量。

2.using声明和using编译指令有何区别？

using声明使得名称空间中的单个名称可用，其作用域与using所在的声明区域相同。using编译指令使名称空间中的所有名称可用。使用using编译指令时，就像在一个包含using声明和名称空间本身的最小声明区域中声明了这些名称一样。

3.重新编写下面的代码，使其不使用using声明和using编译指令。

>     #include <iostream>
>     using namespace std;
>     
>     int main()
>     {
>            double x;
>            cout << "Enter value: ";
>            while (!(cin >> x))
>            {
>                 cout << "Bad input. Please enter a number: ";
>                 cin.clear();
>                 while (cin.get() != '\n')
>                     continue;
>            }
>     
>            cout << "Value = " << x << endl;
>            return 0;
>     }

不使用using声明和using编译指令：

#include <iostream>
    
    int main()
    {
        double x;
        std::cout << "Enter value: ";
        while (!(std::cin >> x))
        {
            std::cout << "Bad input. Please enter a number: ";
            std::cin.clear();
            while (std::cin.get() != '\n')
                continue;
        }
    
        std::cout << "Value = " << x << std::endl;
        return 0;
    }

4.重新编写下面的代码，使之使用using声明，而不是using编译指令。

>     #include <iostream>
>     
>     using namespace std;
>     int main()
>     {
>            double x;
>            cout << "Enter value: ";
>            while (!(cin >> x))
>            {
>                cout << "Bad input. Please enter a number: ";
>                cin.clear();
>                while (cin.get() != '\n')
>                    continue;
>            }
>            cout << "Value = " << x << endl;
>            return 0;
>     }

使用using声明：

#include <iostream>
    
    using std::cin;
    using std::cout;
    using std::endl;
    
    int main()
    {
        double x;
        cout << "Enter value: ";
        while (!(cin >> x))
        {
            cout << "Bad input. Please enter a number: ";
            cin.clear();
            while (cin.get() != '\n')
                continue;
        }
        cout << "Value = " << x << endl;
        return 0;
    }

5.在一个文件中调用average(3,6)函数时，它返回两个int参数平均值，在同一个程序的另一个文件中调用时，它返回两个int参数的double平均值。应如何实现？

在每个文件中使用静态函数定义。或者每个文件都在未命名空间中定义一个合适的average函数。

6.下面的程序由两个文件组成，该程序显示什么内容？

>     //file1.cpp
>     #include <iostream>
>     
>     using namespace std;
>     void other();
>     void another();
>     int x = 10;
>     int y;
>     int main()
>     {
>            cout << x << endl;
>            {
>                int x = 4;
>                cout << x << endl;
>                cout << y << endl;
>            }
>            other();
>            another();
>            return 0;
>     }
>     
>     void other()
>     {
>            int y = 1;
>            cout << "Other: " << x << ", " << y << endl;
>     }
> 
>     //file2.cpp
>     #include <iostream>
>     
>     using namespace std;
>     extern int x;
>     
>     namespace
>     {
>            int y = -4;
>     }
>     
>     void another()
>     {
>            cout << "another() " << x << ", " << y << endl;
>     }

10
    4
    0
    Other:: 10, 1
    another() 10, -4

7.下面的代码将显示什么内容？

>     #include <iostream>
>     
>     using namespace std;
>     
>     void other();
>     namespace n1
>     {
>            int x = 1;
>     }
>     
>     namespace n2
>     {
>            int x = 2;
>     }
>     
>     int main()
>     {
>            using namespace n1;
>            cout << x << endl;
>            {
>                int x = 4;
>                cout << x << ", " << n1::x << ", " << n2::x << endl;
>            }
>            using n2::x;
>            cout << x << endl;
>            other();
>            return 0;
>     }
>     void other()
>     {
>            using namespace n2;
>            cout << x << endl;
>            {
>                int x = 4;
>                cout << x << ", " << n1::x << ", " << n2::x << endl;
>            }
>            using n2::x;
>            cout << x << endl;
>     }

1
    4, 1, 2
    2
    2
    4, 1, 2
    2

## 三、编程练习 ##

>     // golf.h -- for pe9-1.cpp
>     const int Len = 40;
>     struct golf
>     {
>            char fullname(Len);
>            int handicap;
>     };
>     // non-interactive version:
>     // function sets golf structure to provided name, handicap
>     // using values passed as arguments to the function
>     void setgolf(golf & g, const char * name, int hc);
>     // interactive version:
>     // function solicits name and handicap from uaer
>     // and sets the members of g to the valus entered
>     // returns 1 if name is entered, 0 if name is empty string
>     int setgolf(golf & g);
>     // function resets handicap to new value
>     void handicap(golf & g, int hc);
>     // function displays  contents of golf structure
>     void showgolf(const golf &g);

注意到setgolf()被重载，可以这样使用其第一个版本：

>     golf ann;
>     setgolf(ann, "Ann Birdfree", 24);

上述函数调用提供了存储在ann结构中的信息。可以这样使用其第二个版本：

>     golf andy;
>     setgolf(andy);

上述函数将提示用户输入姓名和等级，并将它们存储在andy结构中。这个函数可以（但是不一定必须）在内部使用第一个版本。

根据这个头文件，创建一个多文件程序。其中的一个文件名为golf.cpp，它提供了与头文件中的原型匹配的函数定义；另一个文件应包含main()，并演示原型化函数的所有特性。例如，包含一个让用户输入的循环，并使用输入的数据来填充一个由golf结构组成的数组，数组被填满或用户将高尔夫选手的姓名设置为空字符串时，循环将结束。main()函数只使用头文件中原型化的函数来访问golf结构。

golf.cpp:

#include "golf.h"
    #include <iostream>
    
    using namespace std;
    
    void setgolf(golf &g, const char *name, int hc)
    {
        strcpy(g.fullname, name);
        g.handicap = hc;
    }
    
    int setgolf(golf &g)
    {
        cout << "please enter fullname : ";
        cin.getline(g.fullname, Len);
        if (strlen(g.fullname) == 0)
            return 0;
        else
        {
            cout << "please enter handicap : ";
            cin >> g.handicap;
            cin.get();
            return 1;
        }
    }
    
    void handicap(golf &g, int hc)
    {
        g.handicap = hc;
    }
    
    void showgolf(golf &g)
    {
        cout << "fullname : " << g.fullname << ", handicap : " << g.handicap << endl;
    }

main.cpp:

#include "golf.h"
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
        golf ann, andy, arrGolf[3];
        setgolf(ann, "Ann Birdfree", 24);
        showgolf(ann);
    
        if (setgolf(andy) == 1)
            showgolf(andy);
        handicap(andy, 20);
        showgolf(andy);
    
        int i = 0;
        while (i < 3 && setgolf(arrGolf[i]))
        {
            showgolf(arrGolf[i]);
            i++;
            if(i<3)
            cout << "next one: " << endl;
        }
        return 0;
    }

2.修改程序清单9.9：

>     //Listing 9.9 static.cpp
>     // static.cpp -- using a static local variable
>     #include <iostream>
>     // constants
>     const int ArSize = 10;
>     // function prototype˜
>     void strcount(const char *str);
>     int main()
>     {
>         using namespace std;
>         char input[ArSize];
>         char next;
>         cout << "Enter a line:\n";
>         cin.get(input, ArSize);
>         while (cin)
>         {
>     
>             cin.get(next);
>             while (next != '\n') // string didn't fit!
>                 cin.get(next);   // dispose of remainder strcount(input);
>             cout << "Enter next line (empty line to quit):\n";
>             cin.get(input, ArSize);
>         }
>         cout << "Bye\n";
>         return 0;
>     }
>     void strcount(const char *str)
>     {
>         using namespace std;
>         static int total = 0;
>         int count = 0;
>         // static local variable // automatic local variable
>         cout << "\"" << str << "\" contains ";
>         while (*str++) // go to end of string
>             count++;
>         total += count;
>         cout << count << " characters\n";
>         cout << total << " characters total\n";
>     }

用string对象代替字符数组。这样，该程序将不再需要检查输入的字符串是否过长，同时可以将输入字符串同字符串“”进行比较，以判断是否为空行。

#include <iostream>
    #include <string>
    void strcount(const std::string &str);
    
    int main()
    {
        using namespace std;
        string input;
        cout << "Enter a line:\n";
        getline(cin, input);
        while (input.size())
        {
            strcount(input);
            cout << "Enter next line (empty line to quit):\n";
            getline(cin, input);
        }
        cout << "Bye\n";
        return 0;
    }
    void strcount(const std::string &str)
    {
        using namespace std;
        static int total = 0;
        int count = str.size();
        cout << "\"" << str << "\" contains ";
        total += count;
        cout << count << " characters\n";
        cout << total << " characters total\n";
    }

3.下面是一个结构声明：

>     struct chaff
>     {
>          char dross[20];
>          int slag;
>     };

编写一个程序，使用定位new运算符将一个包含两个这种结构的数组放在一个缓冲区中。然后，给结构的成员赋值（对于char数组，使用函数strcpy()），并使用一个循环来显示内容。一种方法是像程序清单9.10那样将一个静态数组用作缓冲区；另一种方法是使用常规new运算符来分配缓冲。

#include <iostream>
    using namespace std;
    
    const int LEN = 512;
    const int N = 3;
    char buff[LEN];
    
    struct chaff
    {
        char dross[20];
        int slag;
    };
    
    int main()
    {
        chaff *cf1 = new chaff[N];
        chaff *cf2 = new (buff) chaff[N];
        string temp;
        for (int i = 0; i < N; i++)
        {
            cout << "Please enter dross of #" << i + 1 << " chaff :";
            cin.getline(cf1[i].dross, 20);
            strcpy(cf2[i].dross, cf1[i].dross);
            cout << "enter slag :";
            cin >> cf1[i].slag;
            cf2[i].slag = cf1[i].slag;
            cin.ignore();
        }
        for (int i = 0; i < N; i++)
        {
            cout << "#" << i + 1 << " chaff:" << endl;
            cout << "cf1[" << i << "].dross : " << cf1[i].dross << ", slag :"
                 << "cf1[" << i << "].slag : " << cf1[i].slag << endl;
            cout << "cf2[" << i << "].dross : " << cf2[i].dross << ", slag :"
                 << "cf2[" << i << "].slag : " << cf2[i].slag << endl;
        }
        return 0;
    }

4。请基于下面这个名称空间编写一个由3个文件组成的程序：

namespace SALES
    {
        const int QUARTERS = 4;
        struct Sales
        {
            double sales [QUARTERS];
            double average;
            double max;
            double min;
        };
        // copies the lesser of 4 or n items from the array ar
        // to the sales member of s and computes and stores the 
        // average, maximum, and minimum values of the entered items;
        // remaining elements of sales ,if any, set to 0
        void setSales(Sales & s,const double ar[],int n);
        // gathers sales for 4 quarters interactively,stores them
        // in the sales member of s and computes and stores the
        // average,maximum,and minimum values
        void setSales (Sales & s);
        // display all information in structure s
        void showSales(const Sales & s);
    }

第一个文件是一个头文件，其中包含名称空间：第二个文件是一个源代码文件，它对这个名称空间进行扩展，以提供这三个函数的定义；第三个文件声明两个Sales对象，并使用setSales（）的交互式版本为一个结构提供值，然后使用setSales（）的非交互式版本为另一个结构提供值。另外它还使用showSales（）来显示这两个结构的内容。

1.sales.h

//sales.h-----头文件
    namespace SALES
    {
        const int QUARTERS = 4;
        struct Sales
        {
            double sales [QUARTERS];
            double average;
            double max;
            double min;
        };
        void setSales(Sales & s,const double ar[],int n);
        void setSales (Sales & s);
        void showSales(const Sales & s);
    }

2.sales.cpp

//sales.cpp-----源代码文件
    #include "sales.h"
    
    using namespace std;
    namespace SALES
    {
        void setSales(Sales &s, const double ar[], int n)
        {
            double min = 0, max = 0, sum = 0;
            s.min = s.max = ar[0];
            for (int i = 0; i < n; i++)
            {
                s.sales[i] = ar[i];
                sum += ar[i];
                if (ar[i] > max)
                {
                    max = ar[i];
                }
                if (ar[i] < min)
                {
                    min = ar[i];
                }
            }
            s.average = sum / n;
        }
    
        void setSales(Sales &s)
        {
            cout << "Please enter 4 quarters for sales:" << endl;
            cout << "the 1 quarter :";
            cin >> s.sales[0];
            s.min = s.max = s.sales[0];
            for (int i = 1; i < 4; i++)
            {
                cout << "the " << i << " quarter :";
                cin >> s.sales[i];
                if (s.max < s.sales[i])
                {
                    s.max = s.sales[i];
                }
                if (s.min > s.sales[i])
                {
                    s.min = s.sales[i];
                }
            }
            s.average = (s.sales[0] + s.sales[1] + s.sales[2] + s.sales[3]) / 4;
        }
    
        void showSales(const Sales &s)
        {
            cout << "Display all information in sales : " << endl;
            cout << "The 4 quarters are $" << s.sales[0] << ", $" << s.sales[1] << ", $" << s.sales[2] << ", $" << s.sales[3] << endl;
            cout << "The average income is $" << s.average << endl;
            cout << "The maximum income is $" << s.max << endl;
            cout << "The minimum income is $" << s.min << endl;
        }
    }

3.main.cpp

#include "sales.h"
    #include <iostream>
    
    using namespace SALES;
    int main()
    {
        double arr[4] = {3.4, 5.6, 2.5, 6.1};
        Sales s1, s2;
        setSales(s1, arr, 4);
        showSales(s1);
        setSales(s2);
        showSales(s2);
        return 0;
    }

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