C++ primer plus 第六版 第七章 编程练习答案

第七章 编程练习答案

这是第一次把课后编程写出来记录，答案基本都是自己的想法加参考书中的例子，不过部分类型的写法和输入输出不懂，参考了别人的的代码。以后要及时记录代码，并且注释明白，感觉这样会加深理解。希望以后看到能够轻松搞明白。

1

#include 
using namespace std;
double tiaohe (double x, double y);

int main() 
{
    double x, y, z;
    cout << "Enter two numbers (0 to quit): " << endl;
    cin >> x;
	cin >> y;
    while ( x != 0 && y != 0)
    {
        z = tiaohe(x, y);
        cout << z << endl;
        cout << "Enter two numbers (0 to quit): " << endl;
        cin >> x >> y;
    } 
	cout << "Done." << endl;
	   
    return 0;
}

double tiaohe (double x, double y)
{
    double ans;
    ans = 2.0 * x * y / ( x + y);
    return ans;
}

2

#include 

using namespace std;

const int Max = 10;

void show(double arr[], int n);
double sum(double arr[], int n);

int main ()
{
	
	double average;
	double arr[Max];
	
	cout << "Please enter golf scores.\n";
	cout << "You may enter up to " << Max
	     << " golf scores.\n";
	cout << "score #1: ";
//get data	
	int i = 0;
	int n = 0;
	while (i < Max && cin >> arr[i])
	{
		if (++i < Max)
		    cout << "score #" << i+1 << ": ";
		n++;
	};
	cout << "\nThe result of golf scores: " << endl;
//calculate average, report result	
    show(arr, n);
    average = sum(arr, n) /n;
	cout << "\nThe average of golf scores: " << average << "\n";
	
	return 0;	
}

void show(double arr[], int n)
{
	int total = 0;
	for(int i = 0; i < n; i++)
	{
		cout << "score #" << i+1 << ": ";
	   	cout << arr[i] << endl;	
	}
}

double sum(double arr[], int n)
{
	double total = 0;
	for(int i = 0; i < n; i++)
	    total = total + arr[i];
	return total;
}

3

#include 

using namespace std;

struct box
{
	char maker[40];
	float height;
	float width;
	float length;
	float volume;
};

void show(box Alex);//按值传递结构 
void show_volume(box * p_box);// 传递结构的地址 

int main ()
{
	box Alex;
	
	cout << "Enter the maker: " << endl;
	cin.get( Alex.maker, 40);
	cin.get();//注意字符输入 
	cout << "Enter the height: " << endl;
	cin >> Alex.height;
	cout << "Enter the width: " << endl;
	cin >> Alex.width;
	cout << "Enter the length: " << endl;
	cin >> Alex.length;			
	
	show_volume(&Alex);
	show(Alex);
	
	return 0;
}
//函数a 
void show(box Alex)
{
	cout << "\nThe maker is: ";
	cout << Alex.maker << endl;
	cout << "The height is: ";
	cout << Alex.height << endl;
	cout << "The width is: ";	
	cout << Alex.width << endl;
	cout << "The length is: ";
	cout << Alex.length << endl;
	cout << "The volume is: ";
	cout << Alex.volume << endl;		
}
//函数b 
void show_volume(box * p_box)
{
	p_box->volume = p_box->height * p_box->width * p_box->length;
}

4

#include 
long double probability(unsigned numbers, unsigned picks, int special);
using namespace std;

int main()
{
	double total, choices, s;
	cout << "Enter the find number of choices on the game card, the number\n"
	        "of picks allowedand and the special number:\n";
	while((cin >> total >> choices >> s) && choices <= total)//输入条件 
	{
		cout << "You have one chance in ";
		cout << probability(total, choices, s);
		cout << " of winning.\n";
		cout << "Next two numbers (q to quit): ";
	}
	cout << "bye!\n";
	return 0;
}

long double probability(unsigned numbers, unsigned picks, int s)
{
	long double result = 1.0;
	long double n;
	unsigned p;
	
	for (n = numbers, p = picks; p > 0; n--, p--)
	    result = result * n / p ;//减小中间变量 
	result = result * s; 
	return result;
}

5

#include

using namespace std;

long int factorial(int n);//函数声明

int main()
{
	int x;
	long int ans;
	cout << "Please enter the number: (q to quit)" << endl;
	
	while(cin >> x)//控制输入条件，非数字时结束 
	{

	cout << "The factorial is: "<< factorial(x) << endl;				
		
	}
	cout << "Over." << endl;

	return 0;
}
//递归思想 
long int factorial(int n)
{
	long int ans;
	if (n >0)
		ans = n * factorial(n-1);
	if (n == 0)
	    ans = 1;
	return ans;
}

6

#include 

using namespace std;
//函数声明 
int Fill_array(double * p_arr, int n);
void Show_array(double * p_arr, int n);
void Reverse_array(double * p_arr, int bagin, int end, int n);

int main()
{
	int n, size;

	cout << "Please enter the number of array: " << endl;
	
	cin >> size;
	
	double * p_arr = new double[size];
	//未修改前的代码double arr[size];
			
	n = Fill_array(p_arr, size);
		
	Show_array(p_arr, n);
	
    Reverse_array(p_arr, 0, n-1, n);
	
	Show_array(p_arr, n);	
	
    Reverse_array(p_arr, 1, n-2, n);//除首尾元素外进行交换 
	
	Show_array(p_arr, n);	
		
	cout << "Over.\n";
	
	return 0;
}

//填充函数 
int Fill_array(double * p_arr, int n)
{
	int count = 0;
	cout << "Please enter the array: " << endl;	
	for(int i = 0; i < n && cin >> p_arr[i]; i++)//注意输入条件 
	{
		count++;		
	}	
	
	return count;
}

//显示函数 
void Show_array(double * p_arr, int n)
{
	cout << "Now, the array is: " << endl;
	for(int i = 0; i < n; i++)
	{
		cout << p_arr[i] << " ";		
	}
	cout << endl;
}

//反转函数 
void Reverse_array(double * p_arr, int begin, int end, int n)//注意参数起止 
{
	double t;//原来这里是int类型，经提醒后修改
	for(int i = begin; i < n/2; i++)
	{
		t = p_arr[i];		
		p_arr[i] = p_arr[begin + end - i];//注意参数起止对交换的影响	
		p_arr[begin + end - i] = t;		
	}	
}

7

#include 

using namespace std;

const int Max = 5;
double * fill_array(double * p_begin, double * p_end);//如何用两个指针表示区间 
void show_array(double * p_begin, double * p_end);//注意这里的类型要前后一致 
void revalue(double r, double * p_begin, double * p_end);

int main()
{

	double properties[Max];
	
	double * pt = fill_array(properties, properties + Max);
	
	show_array(properties, pt);
	
	if (properties != pt)//当首尾地址不同，即存在区间时 
	{
		cout << "Enter revaluation factor: ";
		double factor;
		while(!(cin >> factor))//输入错误时返回false值，取反执行该操作 
		{
			cin.clear();
			while (cin.get() != '\n')
			    continue;
			cout << "Bad input: Please enter a number: ";
		}
		revalue(factor, properties, pt);
		show_array(properties, pt);
	}
	cout << "Done.\n";
	return 0;
		
}

//填充数组 
double * fill_array(double * p_begin, double * p_end)
{
	int i = 1;
	double * pt;
	for (pt = p_begin; pt != p_end; pt++, i++)
	{
		cout << "Enter value #" << i << ": ";
		cin >> *pt;
//-----------输入非数字和负数的情况------------------------ 
		if (!cin)
		{
			cin.clear();
			while (cin.get() != '\n')
			    continue;
			cout << "Bad input; input process terminated.\n";
			break;
		}
		else if (*pt < 0)
		    break;
	}
//-----------传递指针,注意这里传递的是地址，要用&---------- 	
	return &(*pt);
}


//显示数组 
void show_array(double * p_begin, double * p_end)
{
	int i = 1;
	double * pt;
	for (pt = p_begin; pt != p_end; pt++, i++)//注意这里用指针传递
	{
		cout << "Property #" << i << ": $";
		cout << *pt << endl;
	}
}

//修改数组 
void revalue(double r, double * p_begin, double * p_end)
{

	for (double * pt = p_begin; pt != p_end; pt++)
		*pt *= r;
}

8

a.

#include 

using namespace std;

const int Seasons = 4;
const char * p_season[Seasons] = {"Spring", "Summer", "Fall", "Winter"};

void fill(double * pa);
void show(double * da);

int main()
{
    double expenses[Seasons];
    
	fill(&expenses[Seasons]);//注意传递地址 
	
	show(&expenses[Seasons]);
	
	return 0;
	
}

void fill(double * pa)
{
	for(int i = 0; i < Seasons; i++)
	{
		cout << "Enter " << *(p_season + i) << " expenses: ";
		cin >> pa[i];//注意这里pa[i]等价于*(pa+i),即数组名实际为一个指针 
	}	
}

void show(double * da)
{
	double total = 0.0;
	cout << "\nEXPENSES\n";
	for(int i = 0; i < Seasons; i++)
	{
		cout << *(p_season + i) << ": $" << da[i]<< endl;
		total += da[i];//解释同上 
	}	
	cout << "Total Expenses: $" << total << endl;	
} 

b.

#include 
struct expenses{
	double money;
};//定义结构 

using namespace std;

const int Seasons = 4;
const char * p_season[Seasons] = {"Spring", "Summer", "Fall", "Winter"};

void fill(double * pa);
void show(double * da);

int main()
{
    expenses use[Seasons];//声明结构 
    
	fill(&use[Seasons].money);//注意传递地址 
	
	show(&use[Seasons].money);
	
	return 0;
	
}

//------------调用函数不需要修改--------------- 
void fill(double * pa)
{
	for(int i = 0; i < Seasons; i++)
	{
		cout << "Enter " << *(p_season + i) << " expenses: ";
		cin >> *(pa+i);//注意这里pa[i]等价于*(pa+i),即数组名实际为一个指针 
	}	
}

void show(double * da)
{
	double total = 0.0;
	cout << "\nEXPENSES\n";
	for(int i = 0; i < Seasons; i++)
	{
		cout << *(p_season + i) << ": $" << da[i]<< endl;
		total += da[i];//解释同上 
	}	
	cout << "Total Expenses: $" << total << endl;	
} 

9

#include 

using namespace std;

const int SLEN = 30;
struct student {
	char fullname[SLEN];
	char hobby[SLEN];
	int ooplevel;
};
 
int getinfo(student pa[], int n);
void display1(student st);
void display2(const student * ps);
void display3(const student pa[], int n);

int main()
{
	cout << "Enter class size: ";
	int class_size;
	cin >> class_size;
	while (cin.get() != '\n')
	    continue;
	    
	student * ptr_stu = new student[class_size];
	int entered = getinfo(ptr_stu, class_size);
	for (int i = 0; i < entered; i++)
	{
		display1(ptr_stu[i]);
		display2(&ptr_stu[i]);
	}
	display3(ptr_stu, entered);
	delete [] ptr_stu;
	cout << "Done\n";
	return 0;	
}

//获取数据，注意获得字符和数字的不同 
int getinfo(student pa[], int n)//pa[]可以视作指针 
{
	int count = 0; 
	cout << "\nEnter the student information：" << endl;
	for(int i = 0; i < n ;i++)
	{
		cout << "Student #" << i+1 << ": " << endl;
		cout << "Enter the fullname: " ;	
		cin.getline(pa[i].fullname, SLEN);
		cout << "Enter the hobby: " ;
		cin.getline(pa[i].hobby, SLEN);
		cout << "Enter the ooplevel: " ;		
		cin >> pa[i].ooplevel;
		if(!cin)break;//非数字时提前终止输入 
		cin.get();
		count++;
	}
    cout<<"Enter end!" << endl << endl;  			
    return count;	
}

void display1(student st)
{
	cout << "The fullname: " << st.fullname << endl;	
	cout << "The hobby: " << st.hobby << endl;
	cout << "The ooplevel: " << st.ooplevel << endl;
	cout << endl;
}

void display2(const student * ps)
{
	cout << "The fullname: " << ps->fullname << endl;	
	cout << "The hobby: " << ps->hobby << endl;
	cout << "The ooplevel: " << ps->ooplevel << endl;
	cout << endl;	
}


void display3(const student pa[], int n)
{
	cout << "\nHere is the student information：" << endl;	
	for(int i = 0; i < n; i ++)
	{
	cout << "Student #" << i+1 << ": " << endl;
	cout << "The fullname: " << pa[i].fullname << endl;	
	cout << "The hobby: " << pa[i].hobby << endl;
	cout << "The ooplevel: " << pa[i].ooplevel << endl;						
	}	
}

==

#include 

using namespace std;

double calculate (double a, double b, double (*p)(double a, double b));//注意声明 
double add (double a, double b);
double subtract (double a, double b);
double multiply (double a, double b);
double divide (double a, double b);

int main()
{
	double a, b;
	double (*pf[4])(double a, double b);
	pf[0] = add;
	pf[1] = subtract;
	pf[2] = multiply;
	pf[3] = divide;
	
	cout << "Enter two numbers: (q to quit)" << endl;
	while(cin >> a >> b)
	{
	    for(int i = 0 ; i < 4 ; i++)
	       cout << "The answer is: "<< (*pf[i])(a, b) << endl;			
	}
	cout << "Done!" << endl;
	return 0;
}

//函数原型，加减乘除 
double calculate (double a, double b, double (*p)(double a, double b))
{	
	return (*p)(a,b);	
}


double add (double a, double b)
{
	return a + b;
}

double subtract (double a, double b)
{	
	return a - b;		
}

double multiply (double a, double b)
{	
	return a * b;		
}

double divide (double a, double b)
{	
	return a / b;		
}