《C++ Primer Plus（第六版）》（9）（第七章 函数 笔记和答案）

1.ANSI C是C语言的标准，任何C语言的编译器都在ANSI C的基础上扩充。
ANSI C几乎不能完成任何程序的开发。TC、VC等都对ANSI C进行了扩充，加入了自己的规则和库之类的。

对于函数头：

void fun();

在ANSI C中，意味着不指出参数，后面定义参数列表。

而C++则是表示没有函数，要是想不指出参数表，应该用省略号

void fun(...);

2.C++标准使用参数（argument）来表示实参，使用参量（parameter）来表示形参

3.带const的二级指针和非const的一级指针混合使用的时候将不安全，先看个代码

const int **pp2;
int * p1;
const int n = 13;
pp2 = &p1;//这里会报错，如果这里成功的话，
*pp2 = &n;
*p1 = 10;//这里就修改了常量

会报错：

error C2440: “=”: 无法从“int **”转换为“const int **”

所以：当且仅当只有一层间接关系的时候（如指针指向基本数据类型）时，才可以将非const的地址或者指针赋值给const指针。

4.指向常量的指针，是可以改变指针指向的地址。

int a = 1;
int b = 2;
const int * p = &a;
p = &b;//这个是合法的，当然不能通过p修改a和b的值。
int* const p2 = &a;
p2 = &b;//这个不合法，不能修改指针的内容

5.C++不允许main()调用自己。C好像可以

6.函数也有指针，函数的名字就是它的指针

int fun()
{
return 0;
}

void CChapter2Answer::answer()
{
cout << fun << endl;
}

这样输出的就是函数的指针。怪不得函数名不能跟变量名相同。

要指向函数的指针，要编写对应的函数原型的指针。

因为C++是强类型语言，所以把函数地址作为参数传递到别的函数中，是非常麻烦的。怪不得这么少见，而Lua这种弱类型语言则到处都是这种处理。

看了书上的介绍，函数指针真的挺繁琐，但是因为这本书是基础的，所以没有提到在哪里比较有用。

7.12复习题

1.定义函数，提供原型，调用函数，（居然不是声明、实现、调用）

2.

void igor();
float tofu(int i);
double mpg(double a , double b);
long summation(long a[], int num);
double doctor(const char* a);
void ofcourse(boss b);
char* plot(map* m);

3.

void fun3(int a[], int size, int b)
{
for (int i = 0; i < size; i++)
{
a[i] = b;
}
}

4.

void fun4(int a[], int b[], int c)
{
for (int* i = a; i != b; i++)
{
*i = c;
}
}
void CChapter2Answer::answer()
{
int a[8] = { 1, 2, 3, 4, 5, 6, 7, 8 };
fun4(a, a + 8, 1);
}

5.

double fun5(const double a[], int b )
{
double md = 0;
for (int i = 0; i < b; i++)
{
if (i == 0)
{
md = a[i];
}
else if (md < a[i])
{
md = a[i];
}
}
return md;
}
void CChapter2Answer::answer()
{
double a[8] = { 1, 2, 3, 4, 5, 6, 7, 8 };
cout << fun5(a, 8 ) << endl;
}

6.将const限定符用于指针，以防止指向的原始数据被修改。程序传递的基本类型时，将按值传递，函数使用副本。修改对原始数据没有影响。

7.char* a，char a[]，带""的字符串常量

8.

double replace(char * str, char c1, char c2 )
{
int count = 0;
while (*str != 0)
{
if (*str == c1)
{
*str = c2;
++count;
}
++str;
}
return count;
}
void CChapter2Answer::answer()
{
char str[80] = "fsajasdaaffafsaaereacsd";//这里用char*,在函数里面赋值的时候就报错了。
replace(str, 'a', 'l');
}

写这个让我明白，char*和char[]还是有所不同的。用char*等于一个字符串常量的时候，这里面的东西是不能修改的。

用char[]的时候，自己保存了一份内存，可以修改。

9.字符串可以看做它本身的地址，也是第一个字符的地址。所以*"pizza"的值是p，"taco"[2]则是c

cout << *"pizza" << endl;
cout << "taco"[2] << endl;

结果：

p

c

10.值传递会构建一个副本，单其实这个副本是浅复制的，如果结构里面的属性是指针，也只是复制了地址。如果不允许修改，可能会被改了内容。

指针传递的话修改了肯定会改到的。所以对于函数，很少值传递一个结构的。复制也要花时间和空间啊。

struct STest
{
int a;
int b;
};
int funA( STest a )//值传递
{
return a.a + a.b;
}
int funB(STest* b)//地址传递
{
return b->a + b->a;
}

void CChapter2Answer::answer()
{
STest c;
funA(c);
funB(&c);
}

11.

int fun(const char* a)
{
return 1;
}

int (*funptr)(const char* a);

int judge(int (*funpter)(const char* a));

12.

struct applicant
{
char name[30];
int credit_ratings[3];
};

void printInfo(applicant a)
{
cout << a.name << endl;
for (int i = 0; i < 3; ++i)
{
cout << a.credit_ratings[i] << endl;
}
}

void printInfoEx(applicant* a)
{
cout << a->name << endl;
for (int i = 0; i < 3; ++i)
{
cout << a->credit_ratings[i] << endl;
}
}

void CChapter2Answer::answer()
{
applicant a = { "Fable Game", { 1001, 2002, 3003 } };
printInfo(a);
printInfoEx(&a);
}

13.其实就是复制一下函数头，然后改一下函数名，并加个括号和星号。

struct applicant
{
char name[30];
int credit_ratings[3];
};

void f1(applicant * a);
const char * f2(const applicant * a1, const applicant * a2);

typedef void (*P1)(applicant * a);
typedef const char * (*P2)(const applicant * a1, const applicant * a2);
P1 p1;
P2 p2;
P1 ap[5];
P2 pa[10];

7.13 编程练习
1.

double ave(double a, double b)
{
return 2 * a * b / (a + b);
}
void CChapter2Answer::answer()
{

double a = 0;
double b = 0;
cout << "Please enter digit a:";
cin >> a;
cout << "Please enter digit b:";
cin >> b;
while ( a != 0 && b != 0 )
{
double c = ave(a, b);
cout << "the ave of a, b: " << c << endl;
cout << "Please enter digit a:";
cin >> a;
cout << "Please enter digit b:";
cin >> b;
}
}

2.真心没明白为什么要用到3个数组。。。

void printArr(int a[], int b)
{
for (int i = 0; i < b; ++i)
{
cout << a[i] <<" ";
}
cout << endl;
}

double ave(int a[], int b)
{
double c = 0;
for (int i = 0; i < b; ++i)
{
c += a[i];
}
return c/b;
}
void CChapter2Answer::answer()
{
const int ARRSIZE = 10;
int a[ARRSIZE] = { 0 };
//输入
int actNum = 0;
for (int i = 0; i < ARRSIZE; ++i)
{
cout << "Please enter the score:" ;
int c = 0;
cin >> c;
if (c < 0 || !cin)
{
break;
}
a[i] = c;
++actNum;
}
if (actNum <= 0)
{
cout << "No data" << endl;
return;
}
//显示
int b[ARRSIZE];
memcpy(b, a, sizeof(a));//
printArr(b, actNum);
int c[ARRSIZE];
memcpy(c, a, sizeof(a));//
double d = ave(c, actNum);
cout << "ave: " << d << endl;
}

3.

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

void printInfo(box b)
{
cout << "maker:" << b.maker << endl;
cout << "height:" << b.height << " width:" << b.width << " length:" << b.length << " volume:" << b.volume;
}
void computeVolume(box* b)
{
b->volume = b->height * b->length * b->width;
}

void CChapter2Answer::answer()
{
box b = { "Fable Game", 1, 32, 445, 0 };
computeVolume(&b);
printInfo(b);
}

4.

long double probalility(unsigned numbers, unsigned picks, unsigned otherTotal)
{
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 * otherTotal;
}
void CChapter2Answer::answer()
{
unsigned total, choices, otherTotal;
cout << "Enter the total number of choice on the game card and\n"
"the number of picks allowed and the other total number of choice:\n";
while ((cin >> total >> choices >> otherTotal) && choices <= total)
{
cout << "You have one chance in ";
cout << probalility(total, choices, otherTotal);
cout << " of winning.\n";
cout << "Next three numbers (q ot quit):";
}
cout << "bye\n";

}

5.

long long recursion(unsigned number )
{
if (number <= 1)
{
return 1;
}
else
{
return number * recursion(number - 1);
}

}
void CChapter2Answer::answer()
{
unsigned num;
while ( cin >> num )
{
cout << num << "! = " << recursion(num) << endl;
cout << "Next num (q ot quit):";
}
cout << "bye\n";

}

6.

int fillArray( double a[], int num)
{
cout << "Please enter a double:";
double b;
cin.clear();
cin >> b;
int count = 0;
while (cin && count < num)
{
a[count] = b;
count++;
cout << "Please enter a double:";
cin >> b;
}
return count;
}

void showArray(double a[], int num)
{
cout << "show array:" << endl;
for (int i = 0; i < num; i++)
{
cout << i << " : " << a[i] << endl;
}
}

void reverseArray(double a[], int num)
{
cout << "reverse array" << endl;
double temp;
for (int i = 0; i < num - 1 - i; i++)
{
temp = a[i];
a[i] = a[num - 1 - i];
a[num -1 - i] = temp;
}
}

void CChapter2Answer::answer()
{
const int Size = 20;
double a[Size] = {0};
int actNum = fillArray(a, Size);//填充数组
showArray(a, actNum);//显示数组
reverseArray(a, actNum);//反转数组
showArray(a, actNum);//显示数组
reverseArray(a + 1, actNum - 2);//反转数组
showArray(a, actNum);//显示数组
}

7.

改之前的代码：

const int Max = 5;
int fill_array( double ar[], int limit)
{
double temp;
int i;
for (i = 0; i < limit; 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;
}
return i;
}

void show_array(const double ar[], int n)
{
for (int i = 0; i < n; i++)
{
cout << "Property #" << i + 1 << ": $" << ar[i] << endl;
}
}

void revalue(double r, double ar[], int n)
{
for (int i = 0; i < n; i++)
{
ar[i] *= r;
}
}

void CChapter2Answer::answer()
{
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))
{
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();

}

改之后的代码：
const int Max = 5;
double* fill_array( double ar[], int limit)
{
double temp;
int i;
for (i = 0; i < limit; 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;
}
return ar + i;
}

void show_array(const double* beginPtr, const double* endPtr)
{
for (int i = 0; beginPtr + i != endPtr; i++)
{
cout << "Property #" << i + 1 << ": $" << beginPtr[i] << endl;
}
}

void revalue(double r, double* beginPtr, double* endPtr)
{
for (int i = 0; beginPtr + i != endPtr; i++)
{
beginPtr[i] *= r;
}
}

void CChapter2Answer::answer()
{
double properties[Max];

double* endPtr = fill_array(properties, Max);
show_array(properties, endPtr);
if (properties != endPtr)
{
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, endPtr);
show_array(properties, endPtr);
}
cout << "Done. \n";
cin.get();
cin.get();

}

8.
修改之前的：

const int Seasons = 4;
const std::array<std::string, Seasons> Snames = { "Spring", "Summer", "Fall", "Winter" };

void fill(std::array < double, Seasons> *pa);
void show(std::array<double, Seasons> da);
void CChapter2Answer::answer()
{
std::array<double, Seasons> expenses;
fill(&expenses);
show(expenses);
cin.get();
cin.get();
}

void fill(std::array< double, Seasons> *pa)
{
for (int i = 0; i < Seasons; i++)
{
cout << "Enter " << Snames[i] << " expenses:";
cin >> (*pa)[i];
}
}

void show(std::array<double, Seasons> da)
{
double total = 0.0;
for (int i = 0; i < Seasons; ++i)
{
cout << Snames[i] << ": $" << da[i] << endl;
total += da[i];
}
cout << "Total Expenses: $" << total << endl;
}

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

void fill(double pa[], int num);
void show(double da[], int num);
void CChapter2Answer::answer()
{
double expenses[Seasons];
fill(expenses, Seasons);
show(expenses, Seasons);
cin.get();
cin.get();
}

void fill(double pa[], int num)
{
for (int i = 0; i < num; i++)
{
cout << "Enter " << Snames[i] << " expenses:";
cin >> pa[i];
}
}

void show(double da[], int num)
{
double total = 0.0;
for (int i = 0; i < num; ++i)
{
cout << Snames[i] << ": $" << da[i] << endl;
total += da[i];
}
cout << "Total Expenses: $" << total << endl;
}

b.

const int Seasons = 4;
const char* Snames[Seasons] = { "Spring", "Summer", "Fall", "Winter" };
struct Expenses
{
double e[Seasons];
};
void fill(Expenses* pa);
void show(Expenses* da);
void CChapter2Answer::answer()
{
Expenses e;
fill(&e);
show(&e);
cin.get();
cin.get();
}

void fill(Expenses* pa)
{
for (int i = 0; i < Seasons; i++)
{
cout << "Enter " << Snames[i] << " expenses:";
cin >> pa->e[i];
}
}

void show(Expenses* da )
{
double total = 0.0;
for (int i = 0; i < Seasons; ++i)
{
cout << Snames[i] << ": $" << da->e[i] << endl;
total += da->e[i];
}
cout << "Total Expenses: $" << total << endl;
}

9.
#include <iostream>

using namespace std;

const int SLEN = 30;
struct Student
{
char fullname[SLEN];
char hobby[SLEN];
int ooplevel;
};

int getinfo(Student pa[], int n)
{
int count = 0;
for (int i = 0; i < n; ++i)
{
cout << "Please enter student name:";
cin.getline(pa[i].fullname, 80);
if (strcmp(pa[i].fullname, "") == 0)
{
break;
}
cout << "Please enter student hobby:";
cin.getline(pa[i].hobby, 80);
cout << "Please enter student ooplevel:";
cin >> pa[i].ooplevel;
cin.get();
count++;
}
return count;
}

void display1(Student st)
{
cout << "student[ name: " << st.fullname << " hobby: " << st.hobby << " ooplevel: " << st.ooplevel << "]\n";
}

void display2(const Student* ps)
{
cout << "student[ name: " << ps->fullname << " hobby: " << ps->hobby << " ooplevel: " << ps->ooplevel << "]\n";
}

void display3(const Student pa[], int n)
{
for (int i = 0; i < n; ++i)
{
display2(pa + i);
}
}

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;
}

10.
#include <iostream>

using namespace std;
double add(double a, double b)
{
cout << a + b << endl;
return a + b;
}

double sub(double a, double b)
{
cout << a - b << endl;
return a - b;
}

double mul(double a, double b)
{
cout << a * b << endl;
return a * b;
}

double div(double a, double b)
{
cout << a / b << endl;
return a / b;
}

double calculate(double a, double b, double(*fun)(double, double))
{
return fun(a, b);
}

int main()
{
double(*pf[4])(double, double) = { add, sub, mul, div };
double a, b;
cout << "Please enter a:";
cin >> a;
cout << "Please enter b:";
cin >> b;
while (cin && b != 0)
{
for (int i = 0; i < 4; ++i)
{
calculate(a, b, pf[i]);
}
cout << "Please enter a:";
cin >> a;
cout << "Please enter b:";
cin >> b;
}
return 0;
}