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目录

 

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本章小结

       函数是C++的编程模块。要使用函数，必须提供定义和原型，并调用该函数。函数定义是实现函数功能的代码：函数原型描述了函数的接口：传递给函数的值的数目和种类以及函数的返回类型。函数调用使得程序将参数传递给函数，并执行函数的代码。        在默认情况下，C++函数按值传递参数。这意味着函数定义中的形参是新的变量，它们被初始化为函数调用所提供的值。因此，C++函数通过使用拷贝，保护了原始数据的完整性。         C++将数组名参数视为数组第一个元素的地址。从技术上讲，这仍然是按值传递的，因为指针是原始地址的拷贝，但函数将使用指针来访问原始数组的内容。当且仅当声明函数的形参时，下面两个声明才是等价的： typeName arr[]; typeName * arr;        这两个声明都表明，arr是指向typeName的指针，但在编写函数代码时，可以像使用数组名那样使用arr来访问元素：arr[i]。即使在传递指针时，也可以将形参声明为const指针，来保护原始数据的完整性。由于传递数据的地址时，并不会传输有关数组长度的信息，因此通常将数组长度作为独立的参数来传递。另外，也可以传递两个指针（其中一个指向数组开头，另一个指向数组末尾的下一个元素），以指定一个范围，就像STL使用的算法一样。         C++提供了3种表示C-风格字符串的方法：字符数组、字符串常量和字符串指针。他们的类型都是char*（char指针），因此被作为char*类型参数传递给函数。C++使用空值字符（\0）来结束字符串，因此字符串函数检测空值字符来确定字符串的结尾。        C++还提供了string类，用于表示字符串。函数可以接受string对象作为参数以及将string对象作为返回值，string类的方法size（）可用于判断其存储的字符串的长度。         C++处理结构的方式与基本类型完全相同，这意味着可以按值传递结构，并将其用作函数返回类型。然而，如果结构非常大，则传递结构指针的效率将更高，同时函数能够使用原始数据。这些考虑因素也适用于类对象。         C++函数可以是递归的，也就是说，函数代码中可以包括对函数本身的调用。         C++函数名与函数地址的作用相同。通过将函数指针作为参数，可以传递要调用的函数的名称。  

程序清单

 

7.1  函数简单示例

//calling.cpp -- defining,prototyping,and calling a function#include "stdafx.h"#include
   
    void simple();//function prototypeint main(){	using namespace std;	cout << "main() will call the simple() function:\n";	simple();//function call	cout << "main() is finished with the simple() function.\n";	cin.get();	return 0;}//fuction definitionvoid simple(){	using namespace std;	cout << "I'm but a simple function.\n";}
   

7.2  函数原型与调用

//protos.cpp -- using prototypes and fuction calls#include "stdafx.h"#include
   
    void cheers(int);double cube(double x);using namespace std;int main(){	cheers(5);	cout << "Gibe me a number: ";	double side;	cin >> side;	double volume = cube(side);	cout << "A " << side << " foot cube has a volume of ";	cout << volume << " cubic feet.\n";	cheers(cube(2));	return 0;}void cheers(int n){	for (int i = 0; i < n; i++)		cout << "Cheers! ";	cout << endl;}double cube(double x){	return x * x * x;}
   

7.3  多个参数的函数

//twoarg.cpp -- a function with a arguments#include "stdafx.h"#include
   
    void n_chars(char, int);using namespace std;int main(){	int times;	char ch;	cout << "Enter a character: ";	cin >> ch;	while (ch != 'q')	{		cout << "Enter an integer: ";		cin >> times;		n_chars(ch, times);		cout << "\nEnter another character or press the q-key to quit: ";		cin >> ch;	}	cout << "The value of times is " << times << ".\n";	cout << "Bye\n";	return 0;}void n_chars(char c, int n){	while (n-- > 0)		cout << c;}
   

7.4  多个参数的函数

//lotto.cpp -- probability of winning#include "stdafx.h"#include
   
    //Note:some implementations require double instead of long doublelong double probability(unsigned numbers, unsigned picks);int main(){	using namespace std;	double total, choices;	cout << "Enter the total number of choices on the game card and\nthe number of picks allowed:\n";	while ((cin >> total >> choices) && choices <= total)	{		cout << "You have one chance in ";		cout << probability(total, choices); //compute the odds		cout << " of winning.\n";		cout << "Next two number (q to quit): ";	}	cout << "bye\n";	return 0;}//the following function calculates the probability of picking picks//numbers correctly from numbers choiceslong double probability(unsigned numbers, unsigned picks){	long double result = 1.0; //here come some local variables	long double n;	unsigned p;	for (n = numbers, p = picks; p > 0; n--, p--)		result = result * n / p;	return result;}
   

7.5  参数为数组的函数

//arrfun1.cpp -- functions with an array argument#include "stdafx.h"#include
   
    const int ArSize = 8;int sum_arr(int arr[], int n);int main(){	using namespace std; \	int cookies[ArSize] = { 1,2,4,8,16,32,64,128 };//some systems require preceding int with static to enable array initialization	int sum = sum_arr(cookies, ArSize);	cout << "Total cookies eaten: " << sum << "\n";	return 0;}//return the sum of an integer arrayint sum_arr(int arr[], int n){	int total = 0;	for (int i = 0; i < n; i++)		total = total + arr[i];	return total;}
   

7.6  数组为参数的本质

//arrfun2.cpp -- functions with an array argument#include "stdafx.h"#include
   
    const int ArSize = 8;int sum_arr(int arr[], int n);using namespace std;int main(){	int cookies[ArSize] = { 1,2,4,8,16,32,64,128 };	cout << cookies << " = array address, " << sizeof cookies << " = sizeof cookies\n";	int sum = sum_arr(cookies, ArSize);	cout << "Total cookies eaten: " << sum << endl;	sum = sum_arr(cookies, 3);	cout << "First three eaters ate " << sum << " cookies.\n";	sum = sum_arr(cookies + 4, 4);//cookies+4是第5个元素的地址	cout << "Last four eaters ate " << sum << " cookies.\n";	return 0;}int sum_arr(int arr[], int n){	int total = 0;	cout << arr << " = arr, " << sizeof arr << " = sizeof arr\n";	for (int i = 0; i < n; i++)		total = total + arr[i];	return total;}
   

7.7  多个参数为数组的函数

// arrfun3.cpp -- array functions and const#include "stdafx.h"#include 
   
    const int Max = 5; function prototypesint fill_array(double ar[], int limit);void show_array(const double ar[], int n); // don't change datavoid revalue(double r, double ar[], int n);int main(){	using namespace std;	double properties[Max];	int size = fill_array(properties, Max);	show_array(properties, size);	if (size > 0)	{		cout << "Enter revaluation factor: ";		double factor;		while (!(cin >> factor)) // bad input		{			cin.clear();			while (cin.get() != '\n')				continue;			cout << "Bad input: Please enter a number";		}		revalue(factor, properties, size);		show_array(properties, size);	}	cout << "Done.\n";	cin.get();	cin.get();	return 0;}int fill_array(double ar[], int limit){	using namespace std;	double temp;	int i;	for (i = 0; i < limit; i++)	{		cout << "Enter value #" << (i + 1) << ": ";		cin >> temp;		if (!cin) // bad input		{			cin.clear();			while (cin.get() != '\n')				continue;			cout << "Bad input; input process termianated.\n";			break;		}		else if (temp < 0)			break;		ar[i] = temp;								}	return i;}//the following function can use, but not alter;//the array whose address is ar;void show_array(const double ar[], int n){	using namespace std;	for (int i = 0; i < n; i++)	{		cout << "Property #" << (i + 1) << ": $";		cout << ar[i] << endl;	}}//multiplies each element of ar[] by rvoid revalue(double r, double ar[], int n){	for (int i = 0; i < n; i++)		ar[i] *= r;}
   

7.8  使用数组区间的函数

//arrfun4.cpp -- functions with an array range#include "stdafx.h"#include
   
    const int ArSize = 8;int sum_arr(const int * begin, const int * end);int main(){	using namespace std;	int cookies[ArSize] = { 1,2,4,8,16,32,64,128 };	//some systems require preceding int withe static to enable array initialization	int sum = sum_arr(cookies, cookies + ArSize);	cout << "Total cookies eaten: " << sum << endl;	sum = sum_arr(cookies, cookies + 3);	cout << "First three eaters ate " << sum << " cookies.\n";	sum = sum_arr(cookies + 4, cookies + 8);	cout << "Last four eaters ate " << sum << " cookies.\n";	return 0;}//return the sum of an integer arrayint sum_arr(const int * begin, const int * end){	const int * pt;	int total = 0;	for (pt = begin; pt != end; pt++)		total = total + *pt;	return total;}
   

7.9  C-风格字符串做为参数

//strgfun.cpp -- functions with a string argument#include "stdafx.h"#include
   
    unsigned int c_in_str(const char * str, char ch);int main(){	using namespace std;	char mmm[15] = "minimum";//string in an array	//some systems require preceding char with static to enable array initialization	char const * wail = "ululate";//wail points to string	unsigned int ms = c_in_str(mmm, 'm');	unsigned int us = c_in_str(wail, 'u');	cout << ms << " m characters in " << mmm << endl;	cout << us << " u characters in " << wail << endl;	return 0;}//this function counts the number of ch characters in the string strunsigned int c_in_str(const char * str, char ch){	unsigned int count = 0;	while (*str)//quit when *str is '\0'	{		if (*str == ch)			count++;		str++;//move point to next char	}	return count;}
   

7.10  返回C-风格字符串的函数

//strgback.cpp -- a function that returns a pointer to char#include "stdafx.h"#include
   
    char * buildstr(char c, int n);int main(){	using namespace std;	int times;	char ch;	cout << "Enter a character: ";	cin >> ch;	cout << "Enter an integer: ";	cin >> times;	char *ps = buildstr(ch, times);	cout << ps << endl;	delete[] ps; //free memory	ps = buildstr('+', 20); //reuse pointer	cout << ps << "-DONE-" << ps << endl;	delete[] ps;	return 0;}//builds string made of n c characterschar * buildstr(char c, int n){	char * pstr = new char[n + 1];	pstr[n] = '\0';	while (n-- > 0)		pstr[n] = c;	return pstr;}	return total;}void show_time(travel_time t){	using namespace std;	cout << t.hours << " hours, " << t.mins << " minutes\n";}
   

7.11  传递和返回结构

//travel.cpp -- using structures with functions#include "stdafx.h"#include
   
    struct travel_time{	int hours;	int mins;};const int Mins_per_hr = 60;travel_time sum(travel_time t1, travel_time t2);void show_time(travel_time t);int main(){	using namespace std;	travel_time day1 = { 5,45 };	travel_time day2 = { 4,55 };	travel_time trip = sum(day1, day2);	cout << "Two day total: ";	show_time(trip);	travel_time day3 = { 4,32 };	cout << "Three day total: ";	show_time(sum(trip, day3));	return 0;}travel_time sum(travel_time t1, travel_time t2){	travel_time total;	total.mins = (t1.mins + t2.mins) % Mins_per_hr;	total.hours = t1.hours + t2.hours + (t1.mins + t2.mins) / Mins_per_hr;	return total;}void show_time(travel_time t){	using namespace std;	cout << t.hours << " hours, " << t.mins << " minutes\n";}
   

7.12  处理结构的函数

//strctfun.cpp -- functions with astructure argument#include "stdafx.h"#include
   
    #include
    
     //structure declarationsstruct 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};polar rect_to_polar(rect xypos);void show_polar(polar dapos);int main(){	using namespace std;	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 << "Done.\n";	return 0;}//convert rectangular to polar coordinatespolar 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;}//show polar coordinates, converting angle to degreesvoid 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";}
    
   

7.13  传递结构的地址

//strcptr.cpp -- functions with pointer to structure arguments#include "stdafx.h"#include
   
    #include
    
     //structure templatesstruct 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};void rect_to_polar(const rect * xypos,polar * pda);void show_polar(const polar * pda);int main(){	using namespace std;	rect rplace;	polar pplace;	cout << "Enter the x and y values: ";	while (cin >> rplace.x >> rplace.y) //slick use of cin	{		rect_to_polar(&rplace,&pplace);		show_polar(&pplace);		cout << "Next two numbers (q to quit): ";	}	cout << "Done.\n";	return 0;}//convert rectangular to polar coordinatesvoid rect_to_polar(const rect * pxy,polar * pda){	using namespace std;	pda -> distance = sqrt(pxy -> x * pxy->x + pxy->y * pxy->y);	pda -> angle = atan2(pxy -> y, pxy -> x);}//show polar coordinates, converting angle to degreesvoid show_polar(const polar * pda){	using namespace std;	const double Rad_to_deg = 57.29577951;	cout << "distance = " << pda -> distance;	cout << ", angle = " << pda -> angle * Rad_to_deg;	cout << " degrees\n";}
    
   

7.14  处理string类的函数

//topfive.cpp -- handling an array of string object#include "stdafx.h"#include
   
    #include
    
     using namespace std;const int SIZE = 5;void display(const string sa[], int n);int main(){	string list[SIZE];//an array holding 5string object	cout << "Enter your " << SIZE << " favorite astronomical sights:\n";	for (int i = 0; i < SIZE; i++)	{		cout << i + 1 << ": ";		getline(cin, list[i]);	}	cout << "Your list:\n";	display(list, SIZE);	return 0;}void display(const string sa[], int n){	for (int i = 0; i < n; i++)		cout << i + 1 << ": " << sa[i] << endl;}
    
   

7.15  处理array对象的函数

//arrobj.cpp -- functions with array objects (C++11)#include "stdafx.h"#include
   
    #include
    
     #include
     
      using namespace std;//constant dataconst int Seasons = 4;const array
      
       Snames = { "Spring","Summer","Fall","Winter" };//function to modify array objectvoid fill(array
       
        *pa);//function that uses array object without modifying itvoid show(array
        
          da);int main(){ array
         
           expenses; fill(&expenses); show(expenses); return 0;}void fill(array
          
            * pa){ for (int i = 0; i < Seasons; i++) { cout << "Enter " << Snames[i] << " expenses: "; cin >> (*pa)[i]; }}void show(array
           
             da){ double total = 0.0; cout << "\n\nEXPENSES\n\n"; for (int i = 0; i < Seasons; i++) { cout << Snames[i] << ": $" << da[i] << endl; total += da[i]; } cout << "Total Expenses: $" << total << endl;}
           
          
         
        
       
      
     
    
   

7.16  递归函数

//recur.cpp -- using recursion#include "stdafx.h"#include
   
    void countdown(int n);int main(){	countdown(4);	return 0;}void countdown(int n){	using namespace std;	cout << "Counting down ... " << n << endl;	if (n > 0)		countdown(n - 1); //function calls itself	cout << n << ": Kaboom!\n";}
   

7.17  包含多个递归调用的递归

//ruler.cpp -- using recursion to subdivide a ruler#include "stdafx.h"#include
   
    using namespace std;const int Divs = 6;//the division of rulerconst int Len = 66;//the length of ruler   Len = 2 ^ Divs + 2void subdibide(char ar[], int low, int high, int level);int main(){	char ruler[Len];	int i;	for (i = 1; i < Len - 2; i++)		ruler[i] = ' ';	ruler[Len - 1] = '\0';	int max = Len - 2;	int min = 0;	ruler[min] = ruler[max] = '|';	cout << ruler << endl;	for (i = 1; i <= Divs; i++)	{		subdibide(ruler, min, max, i);		cout << ruler << endl;		for (int j = 1; j < Len - 2; j++)			ruler[j] = ' ';//reset to blank ruler	}	return 0;}void subdibide(char ar[], int low, int high, int level){	if (level == 0)		return;	int mid = (high + low) / 2;	ar[mid] = '|';	subdibide(ar, low, mid, level - 1);	subdibide(ar, mid, high, level - 1);}
   

7.18  函数指针

​//fun_ptr.cpp -- pointers to functions#include "stdafx.h"#include
   
    double betsy(int);double pam(int);//second argument is pointer to a type double function that takes a type int argumentvoid estimate(int lines, double (*pf)(int));int main(){	using namespace std;	int code;	cout << "How many lines of code do you need? ";	cin >> code;	cout << "Here's Betsy's estimate:\n";	estimate(code, betsy);	cout << "Here's Pam's estimate:\n";	estimate(code, pam);	return 0;}double betsy(int lns){	return 0.05*lns;}double pam(int lns){	return 0.03*lns + 0.0004*lns*lns;}void estimate(int lines, double(*pf)(int)){	using namespace std;	cout << lines << " lines will take ";	cout << (*pf)(lines) << " hour(s)\n";//function pointer}​
   

7.19  深入探讨函数指针

//arfupt.cpp -- an array of function pointers#include "stdafx.h"#include
   
    //various notations, same signaturesconst double * f1(const double ar[], int n);const double * f2(const double [], int);const double * f3(const double *, int);int main(){	using namespace std;	double av[3] = { 1112.3, 1542.6, 2227.9 };	const double *(*p1)(const double *, int) = f1;//pointer to a function	auto p2 = f2;	cout << "Using pointers to functions:\n";	cout << " Address Value\n";	cout << (*p1)(av, 3) << ": " << *(*p1)(av, 3) << endl;	cout << p2(av, 3) << ": " << *p2(av, 3) << endl;	const double *(*pa[3])(const double *, int) = { f1,f2,f3 };//pa an array of pointers	auto pb = pa;	cout << "\nUsing an array of pointers to functions:\n";	cout << " Address Value\n";	for (int i = 0; i < 3; i++)		cout << pa[i](av, 3) << ": " << *pa[i](av, 3) << endl;	cout << "\nUsing a pointer to a pointer to a function:\n";	cout << " Address Value\n";	for (int i = 0; i < 3; i++)		cout << pb[i](av, 3) << ": " << *pb[i](av, 3) << endl;	cout << "\nUsing pointers to an array of pointers:\n";	cout << " Address Value\n";	auto pc = &pa;//easy way to declare pc	cout << (*pc)[0](av, 3) << ": " << *(*pc)[0](av, 3) << endl;	const double *(*(*pd)[3])(const double *, int) = &pa;//hard way to declare pd	const double *pdb = (*pd)[1](av, 3);	cout << pdb << ": " << *pdb << endl;	cout << (*(*pd)[2])(av, 3) << ": " << *(*(*pd)[2])(av, 3) << endl;	return 0;}const double * f1(const double * ar, int n){	return ar;}const double * f2(const double ar[], int){	return ar + 1;}const double * f3(const double ar[], int){	return ar + 3;}
   

 

课后编程习题答案

 

//practice.cpp -- this is the practice of the seventh chapter//运行时删除或注释多余部分#include "stdafx.h"#include
   
    //practice-1double t_av(double x, double y);int main(){	using namespace std;	double x, y;	double result;	cout << "Please enter two numbers (0 to stop): ";	while ((cin >> x >> y) && x != 0 && y != 0)	{		result = t_av(x, y);		cout << "The average is: " << result << endl;		cout << "Please enter two numbers (0 to stop): ";	}	return 0;}double t_av(double x, double y){	return 2.0 * x * y / (x + y);}//practice-2const int MAX = 10;using namespace std;int fill_ar(double ar[], int limit);void show_ar(const double ar[], int n);double average(const double ar[], int n);int main(){	double scores[MAX];	int size = fill_ar(scores, MAX);	show_ar(scores, size);	if (size > 0)		cout << "The average of scores is: " << average(scores, size) << endl;	return 0;}int fill_ar(double ar[], int limit){	double temp;	int i;	for (i = 0; i < limit; i++)	{		cout << "Enter score #" << i + 1 << ": ";		cin >> temp;		if (!cin)		{			cin.clear();			while (cin.get() != '\n')				continue;			cout << "Bad input; enter a number: ";			break;		}		if(temp < 0)//输入负数终止输入			break;		ar[i] = temp;	} 	return i;} void show_ar(const double ar[], int n){	for (int i = 0; i < n; i++)		cout << "score #" << i + 1 << ": " << ar[i] << endl;}double average(const double ar[], int n){	double sum = 0.0;	for (int i = 0; i < n; i++)		sum += ar[i];	return sum / n;}//practice-3using namespace std;struct box{	char maker[40];	float height;	float width;	float length;	float volume;};void show(box);box set();box* calculate(box *);int main(){	box a;	a = set();	box* pt = calculate(&a);	show(a);	return 0;} box set(){	box b;	cout << "please input the name of box :";	cin >> b.maker;	cout << "please input the height of box :";	cin >> b.height;	cout << "please input the width of box :";	cin >> b. width;	cout << "please input the length of box :";	cin >> b.length;	b.volume = 0.0;	return b;}void show(box x){	cout << endl << "The height of the box: " << x.height << endl		<< "The width of the box: " << x.width << endl		<< "The length of the box: " << x.length << endl		<< "The volume of the box: " << x.volume << endl;}box* calculate(box* ps){	(*ps).volume = (*ps).height * (*ps).length * (*ps).width;	return ps;}//practice-4using namespace std;long double probability(unsigned, unsigned);int main(){	double a, b, c;	cout << "Enter the number of choices on the game card :";	cin >> a;	cout << "Enter the number of picks allowed in 1 field number:";	cin >> b;	cout << "Enter the number of choices on the game card in 2 field number:";	cin >> c;	while (cin)	{		if (b <= a)		{			long double chance;			chance = probability(a, b)*c;			cout << "You have one chance in "<< chance << " of wining.\n\n";			cout << "Enter the number of choices on the game card :";			cin >> a;			cout << "Enter the number of picks allowed in 1 field number:";			cin >> b;			cout << "Enter the number of choices on the game card in 2 field number:";			cin >> c;			if (!cin)				break;		}		else			break;	} 	cout << "Bye!\n";	return 0;}long double probability(unsigned numbers, unsigned picks){	long double result = 1.0;	long double n;	unsigned p;	for (n = numbers, p = picks; p > 0; n--, p--)		result = result * n / p;	return result;}//practice-5long long int recure(int);int main(){	using namespace std;	int number;	cout << "Enter a integer (q to stop): ";	while (cin >> number)	{		long long int result = recure(number);		cout << number << "! = " << result << endl;		cout << "Next:";	} 	cout << "Done!" << endl;	return 0;}long long int recure(int n){	long long int result;	if (n > 0)		result = n * recure(n - 1);	else		result = 1;	return result;}//practice-6using namespace std;const int Asize = 10;int Fill_array(double[], int);void Show_array(double[], int);double * Reverse_array(double[], int, int);int main(){	double numbers[Asize];	cout << "Please enter some numbers(less than ten): \n";	int i = Fill_array(numbers, Asize);	cout << "You've entered " << i << " numbers:\n";	Show_array(numbers, i);	cout << endl;	double * pt = Reverse_array(numbers, 0, i);	Show_array(pt, i);	cout << endl;	double * ps = Reverse_array(numbers, 1, i);	Show_array(ps, i);	cout << endl;	return 0;}int Fill_array(double ar[], int size){	int i;	for (i = 0; i < Asize; i++)	{		if (cin >> ar[i])			;		else			break;	} 	return i;} void Show_array(double ar[], int size){	for (int i = 0; i < size; i++)		cout << ar[i] << " ";}double * Reverse_array(double ar[], int a, int size){	cout << "Here are(is) the number(s) after reverse:\n";	double temp;	for (int i = a; i < size / 2; i++)	{		temp = ar[i];		ar[i] = ar[size - i - 1];		ar[size - i - 1] = temp;	} 	return ar;}//practice-7using namespace std;const int Max = 5;void show_array(const double[], double *);void revalue(double, double[], double *);double * fill_array(double[], int);int main(){	double properties[Max];	double * p = fill_array(properties, Max);	show_array(properties, p);	if (p != &properties[0])	{		cout << "Enter revaluation factor: ";		double factor;		while (!(cin >> factor))		{			cin.clear();			while (cin.get() != '\n')				continue;			cout << "Bad input; Please enter a number: ";		} 		revalue(factor, properties, p);		show_array(properties, p);	} 	cout << "Done.\n";	return 0;}double * fill_array(double ar[], int n){	double temp;	int i;	for (i = 0; i < n; i++)	{		cout << "Enter value #" << (i + 1) << ": ";		cin >> temp;		if (!cin)		{			cin.clear();			while (cin.get() != '\n')				continue;			cout << "Bad input; input process terminated.\n";			break;		} 		else if (temp < 0)			break;		ar[i] = temp;	}	double * pt = &ar[i - 1];	return pt;} void show_array(const double ar[], double * ps){	const double * p = &ar[0];	for (int i = 0; p != ps + 1; p++, i++)	{		cout << "Property #" << (i + 1) << ": $";		cout << ar[i] << endl;	}} void revalue(double r, double ar[], double * ps){	double * p = &ar[0];	for (int i = 0; p != ps + 1; p++, i++)		ar[i] *= r;}//practice-8ausing namespace std;const char * Seasons[4] = { "Spring", "Summer", "Fall", "Winter" };void fill(double *);void show(double[]);int main(){	double expenses[4];	fill(expenses);	show(expenses);	return 0;} void fill(double ar[]){	double costs;	for (int i = 0; i < 4; i++)	{		cout << "Enter " << Seasons[i] << " expenses: ";		cin >> ar[i];	}} void show(double ar[]){	double total = 0.0;	cout << "\nEXPENSES\n";	for (int i = 0; i < 4; i++)	{		cout << Seasons[i] << ": $" << ar[i] << endl;;		total += ar[i];	} 	cout << "Total Expenses: $" << total << endl;}//practice-8busing namespace std;const char * Seasons[4] = { "Spring", "Summer", "Fall", "Winter" };struct expenditure{	double expenses[4];};expenditure fill(expenditure);void show(expenditure);int main(){	expenditure a = { { 0.0 } };	expenditure v = fill(a);	show(v);	return 0;} expenditure fill(expenditure b){	for (int i = 0; i < 4; i++)	{		cout << "Enter " << Seasons[i] << " expenses: ";		cin >> b.expenses[i];	} 	return b;} void show(expenditure b){	double total = 0.0;	cout << "\nEXPENSES\n";	for (int i = 0; i < 4; i++)	{		cout << Seasons[i] << ": $" << b.expenses[i] << endl;		total += b.expenses[i];	} 	cout << "Total Expenses: $" << total << endl;}//practice-9using 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;}int getinfo(student * p, int num){	int i;	for (i = 0; i < num; i++)	{		cout << "Enter the fullname: ";		cin.getline((p + i)->fullname, SLEN);		cout << "Enter the hobby: ";		cin.getline((p + i)->hobby, SLEN);		cout << "Enter the ooplevel: ";		cin >> (p + i)->ooplevel;		if (!cin)			break;		else			cin.get();	} 	return i;} void display1(student st){	cout << st.fullname << " "		<< st.hobby << " "		<< st.ooplevel << endl;} void display2(const student * ps){	cout << ps->fullname << " "		 << ps->hobby << " "		 << ps->ooplevel << endl;} void display3(const student pa[], int num){	for (int i = 0; i < num; i++)	{		cout << pa[i].fullname << " "			 << pa[i].hobby << " "			 << pa[i].ooplevel << endl;	}}//practice-10double calculate(double x, double y, double(*pf)(double, double));double add(double x, double y);double sub(double x, double y);double mean(double x, double y);int main(){	using namespace std;	double a, b;	double(*pf[3])(double, double) = { add, sub, mean };	char * op[3] = { "add", "sub", "mean" };	cout << "Enter pairs of numbers (q to quit): ";	while (cin >> a >> b)	{		for (int i = 0; i < 3; i++)		{			cout << op[i] << ": " << a << " and " << b << " = "				<< calculate(a, b, pf[i]) << endl;		}	}}double calculate(double x, double y, double(*pf)(double, double)){	return(*pf)(x, y);}double add(double x, double y){	return x + y;}double sub(double x, double y){	return x - y;}double mean(double x, double y){	return(x + y) / 2.0;}​
   

 

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