目录
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<iostream>
void simple();//function prototype
int 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 definition
void 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<iostream>
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<iostream>
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<iostream>
//Note:some implementations require double instead of long double
long 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 choices
long 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<iostream>
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 array
int 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<iostream>
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 <iostream>
const int Max = 5;
function prototypes
int fill_array(double ar[], int limit);
void show_array(const double ar[], int n); // don't change data
void 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 r
void 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<iostream>
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 array
int 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<iostream>
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 str
unsigned 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<iostream>
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 characters
char * 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<iostream>
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<iostream>
#include<cmath>
//structure declarations
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
};
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 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;
}
//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";
}7.13 传递结构的地址
//strcptr.cpp -- functions with pointer to structure arguments
#include "stdafx.h"
#include<iostream>
#include<cmath>
//structure templates
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
};
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 coordinates
void 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 degrees
void 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<iostream>
#include<string>
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<iostream>
#include<array>
#include<string>
using namespace std;
//constant data
const int Seasons = 4;
const array<string, Seasons>Snames = { "Spring","Summer","Fall","Winter" };
//function to modify array object
void fill(array<double, Seasons>*pa);
//function that uses array object without modifying it
void show(array<double, Seasons> da);
int main()
{
array<double, Seasons> expenses;
fill(&expenses);
show(expenses);
return 0;
}
void fill(array<double, Seasons> * pa)
{
for (int i = 0; i < Seasons; i++)
{
cout << "Enter " << Snames[i] << " expenses: ";
cin >> (*pa)[i];
}
}
void show(array<double, Seasons> 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<iostream>
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<iostream>
using namespace std;
const int Divs = 6;//the division of ruler
const int Len = 66;//the length of ruler Len = 2 ^ Divs + 2
void 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<iostream>
double betsy(int);
double pam(int);
//second argument is pointer to a type double function that takes a type int argument
void 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<iostream>
//various notations, same signatures
const 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<iostream>
//practice-1
double 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-2
const 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-3
using 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-4
using 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-5
long 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-6
using 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-7
using 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-8a
using 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-8b
using 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-9
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;
}
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-10
double 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;
}