7.13编程练习

1. 第一题

#include <iostream>
using namespace std;
double average(int, int);


int main() {

    int a, b;
    double s;
    while (cin >> a >> b && a != 0 && b != 0)
    {
        s = average(a, b);
        cout << "调和平均数为：" << s << endl;
    }

    return 0;
}

double average(int a, int b)
{
    return 2.0*a*b/(a+b);
}

运行结果：

2 4
调和平均数为：2.66667
2 2
调和平均数为：2
2 0

2. 第二题

#include <iostream>
using namespace std;
int in(double [], int);
void show(const double [], int);
double average(const double [], int);
const int Max_grade = 10;


int main() {

    double grade[Max_grade];
    int size = in(grade, Max_grade);
    show(grade, size);
    if (size > 0)
    {
        double av = average(grade, size);
        cout << "平均成绩为：" << av << endl;
    }

    return 0;
}

int in(double grade [], int n)
{
    double x;
    int i = 0;
    while (cin >> x && x != -1 && i < Max_grade)
    {
        grade[i++] = x;
    }
    return i;
}

void show(const double arr[], int n)
{
    for (int i=0;i<n;i++)
    {
        cout << "高尔夫成绩为 #" << (i+1) << ": ";
        cout << arr[i];
    }
    cout << endl;
}

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

    return sum / n;
}

运行结果：

99
87
87
-1
高尔夫成绩为 #1: 99高尔夫成绩为 #2: 87高尔夫成绩为 #3: 87
平均成绩为：91

3. 第三题

#include <iostream>
using namespace std;
struct box
{
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};

void a(box x);
void b(box * x);


int main() {

    box fox = {"crazy", 8, 8, 8, 500};
    a(fox);
    b(&fox);

    return 0;
}

void a(box x)
{
    cout << x.maker << endl;
    cout << x.height << endl;
    cout << x.width << endl;
    cout << x.volume << endl;
}

void b(box * x)
{
    x->volume = x->length * x->width * x->height;
    cout << "容量变为：" << x->volume << endl;
}

运行结果：

crazy
8
8
500
容量变为：512

4. 第四题

#include <iostream>
using namespace std;
long double probability(unsigned numbers1, unsigned picks1, unsigned numbers2, unsigned picks2);


int main() {

    double total_1, choices_1, total_2, choices_2;
    cout << "Enter the total number of choices on the game card and
"
            "the number of picks allowed:
";
    while ((cin >> total_1 >> choices_1 >> total_2 >> choices_2) && choices_1 <= total_1 && choices_2 <= total_2)
    {
        cout << "You have one chance in ";
        cout << probability(total_1, choices_1, total_2, choices_2);
        cout << " of winning.
";
        cout << "Next two numbers (q to quit):";
    }
    cout << "bye
";

    return 0;
}

long double probability(unsigned numbers1, unsigned picks1, unsigned numbers2, unsigned picks2)
{
    long double result1 = 1.0, result2 = 1.0;
    long double n1, n2;
    unsigned p1, p2;

    for (n1=numbers1, p1=picks1;p1 > 0;n1--, p1--)
    {
        result1 = result1 * n1 / p1;
    }
    for (n2=numbers2, p2=picks2;p2 > 0;n2--, p2--)
    {
        result2 = result2 * n2 / p2;
    }
    return result1 * result2;
}

运行结果：

Enter the total number of choices on the game card and
the number of picks allowed:
47 5 27 1
You have one chance in 4.14164e+07 of winning.
Next two numbers (q to quit):q
bye

5. 第五题

#include <iostream>
using namespace std;
long jc(int n);


int main() {

    int n;
    long sum=0;
    cout << "请输入一个整数计算阶乘：";
    while (cin >> n)
    {
        sum = jc(n);
        cout << n << "的阶乘为:" << sum << endl;
        cout << "请再次输入数值进行求解：(q to quit)";
    }
    cout << "bye!
";

    return 0;
}

long jc(int n)
{
    if (n == 0 || n == 1)
        return 1;
    if (n > 1)
        return n * jc(n-1);
}

运行结果：

请输入一个整数计算阶乘：4
4的阶乘为:24
请再次输入数值进行求解：(q to quit)5
5的阶乘为:120
请再次输入数值进行求解：(q to quit)q
bye!

6. 第六题

#include <iostream>
using namespace std;
const int Max = 20;
int Fill_array(double arr[], int n);
void Show_array(const double arr[], int n);
void Reverse_array(double * arr, int n);
void Reverse_array_2(double * arr, int n);


int main() {

    double x[Max];
    int size = Fill_array(x, Max);
    Show_array(x, size);
    if (size > 1)
    {
        cout << "完全反转数组：
";
        Reverse_array(x, size);
        cout << "除第一个和最后一个之外反转数组：
";
        Reverse_array_2(x, size);
    }
    else if (size == 1)
    {
        cout << "数组大小为1，反转结果相同
";
    }
    else
    {
        cout << "数组大小为0
";
    }

    return 0;
}

int Fill_array(double arr[], int n)
{
    double x;
    int i = 0;
    while (cin >> x && i < Max)
    {
        arr[i++] = x;
    }
    return i;
}

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

void Reverse_array(double * arr, int n)
{
    double x;
    for (int i=0, j=n-1;i<j;i++, j--)
    {
        x = arr[i];
        arr[i] = arr[j];
        arr[j] = x;
    }
    Show_array(arr, n);
}

void Reverse_array_2(double * arr, int n)
{
    double x;
    for (int i=1, j=n-2;i<j;i++, j--)
    {
        x = arr[i];
        arr[i] = arr[j];
        arr[j] = x;
    }
    Show_array(arr, n);
}

运行结果：

1 2 3 4 5 q
1: 1
2: 2
3: 3
4: 4
5: 5
完全反转数组：
1: 5
2: 4
3: 3
4: 2
5: 1
除第一个和最后一个之外反转数组：
1: 5
2: 2
3: 3
4: 4
5: 1

7. 第七题

#include <iostream>
using namespace std;
const int Max = 5;
double * fill_array(double begin[], int limit);
void show_array(const double * begin, const double * end);
void revalue(double r, double * begin, const double * end);


int main() {

    double properties[Max];

    double * end = fill_array(properties, Max);
    show_array(properties, end);
    if (properties != end)
    {
        cout << "Enter revaluation factor:";
        double factor;
        while (!(cin >> factor))
        {
            cin.clear();
            while (cin.get() != '
')
                continue;
            cout << "Bad input; input process terminated.
";
        }
        revalue(factor, properties, end);
        show_array(properties, end);
    }
    cout << "Done.
";
    cin.get();
    cin.get();

    return 0;
}

double * fill_array(double begin[], 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() != '
')
                continue;
            cout << "Bad input; input process terminated.
";
            break;
        }
        else if (temp < 0)
            break;
        begin[i] = temp;
    }
    return &begin[i];
}

void show_array(const double * begin, const double * end)
{
    const double * pt;
    int i = 0;
    for (pt = begin;pt != end; pt ++)
    {
        cout << "Property #" << (i+1) << ": $";
        cout << *pt << endl;
        i += 1;
    }
}

void revalue(double r, double * begin, const double * end)
{
    double * pt;
    for (pt = begin;pt != end; pt ++)
    {
        *pt *= r;
    }
}

运行结果：（列举了两种情况）

Enter value #1:100000
Enter value #2:80000
Enter value #3:222000
Enter value #4:240000
Enter value #5:118000
Property #1: $100000
Property #2: $80000
Property #3: $222000
Property #4: $240000
Property #5: $118000
Enter revaluation factor:0.8
Property #1: $80000
Property #2: $64000
Property #3: $177600
Property #4: $192000
Property #5: $94400
Done.
Enter value #1:200000
Enter value #2:84000
Enter value #3:160000
Enter value #4:-2
Property #1: $200000
Property #2: $84000
Property #3: $160000
Enter revaluation factor:1.20
Property #1: $240000
Property #2: $100800
Property #3: $192000
Done.

8. 第八题
   a

#include <iostream>
using namespace std;
const int Seasons = 4;
const char * Snames[Seasons] = {
        "Spring", "Summer", "Fall", "Winter"
};

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


int main() {

    double expenses[Seasons];
    fill(&expenses[0]);
    show(expenses);

    return 0;
}

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

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

运行结果：

Enter Spring expenses:212
Enter Summer expenses:256
Enter Fall expenses:208
Enter Winter expenses:244

EXPENSES
Spring: $212
Summer: $256
Fall: $208
Winter: $244
Total Expenses: $920

b

#include <iostream>
using namespace std;
const int Seasons = 4;
const char * Snames[Seasons] = {
        "Spring", "Summer", "Fall", "Winter"
};
struct money
{
    double expenses[Seasons];
};

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


int main() {

    money out{};
    fill(&out);
    show(out);

    return 0;
}

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

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

运行结果：

Enter Spring expenses:212
Enter Summer expenses:256
Enter Fall expenses:208
Enter Winter expenses:244

EXPENSES
Spring: $212
Summer: $256
Fall: $208
Winter: $244
Total Expenses: $920

9. 第九题

#include <iostream>
#include <cstring>
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() != '
')
        continue;

    auto * 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
";

    return 0;
}

int getinfo(student pa[], int n)
{
    char name[SLEN], bo[SLEN];
    int oop;
    int i = 0;
    while (i < n && cin >> name >> bo >> oop && strcmp(name, "") != 0)
    {
        strcpy(pa[i].fullname, name);
        strcpy(pa[i].hobby, bo);
        pa[i].ooplevel = oop;
        i += 1;
    }
    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 n)
{
    for (int i = 0; i < n; ++i)
    {
        cout << pa[i].fullname << " " << pa[i].hobby << " " << pa[i].ooplevel << endl;
    }
}

运行结果：

Enter class size:4
zxc 123 1
asd 456 2
qwe 789 3
rty 741 4
zxc 123 1
zxc 123 1
asd 456 2
asd 456 2
qwe 789 3
qwe 789 3
rty 741 4
rty 741 4
zxc 123 1
asd 456 2
qwe 789 3
rty 741 4
Done

10. 第十题

#include <iostream>
using namespace std;

double calculate(double x, double y, double (*pf)(double x, double y));
double add(double x, double y);
double subtract(double x, double y);
double multiply(double x, double y);
double divide(double x, double y);


int main() {

    int x, y;
    double number[4];
    double (*pf[4])(double x, double y) = {add, subtract, multiply, divide};
    while (cin >> x >> y)
    {
        for (int i = 0;i<4;i++)
        {
            number[i] = calculate(x, y, pf[i]);
        }
        cout << "加减乘除结果分别为：
";
        for (double i : number)
            cout << i << endl;
    }

    return 0;
}

double calculate(double x, double y, double (*pf)(double x, double y))
{
    return pf(x, y);
}

double add(double x, double y)
{
    return x + y;
}

double subtract(double x, double y)
{
    return x - y;
}

double multiply(double x, double y)
{
    return x * y;
}

double divide(double x, double y)
{
    return x / y;
}

运行结果：

2 4
加减乘除结果分别为：
6
-2
8
0.5

1 1
加减乘除结果分别为：
2
0
1
1
q

上面只是提到了指向函数指针的指针，下面我增加了指向该数组指针的指针，看代码：

#include <iostream>
using namespace std;

double calculate(double x, double y, double (*pf)(double x, double y));
double add(double x, double y);
double subtract(double x, double y);
double multiply(double x, double y);
double divide(double x, double y);


int main() {

    int x, y;
    double number[4];
    double (*pf[4])(double x, double y) = {add, subtract, multiply, divide};

    // 1.使用指向函数指针的指针
    while (cin >> x >> y)
    {
        for (int i = 0;i<4;i++)
        {
            number[i] = calculate(x, y, pf[i]);
        }
        cout << "加减乘除结果分别为：
";
        for (double i : number)
            cout << i << endl;
        cout << endl;
    }

    // 上面使用非double型数字跳出后会导致输入流关闭，需要重新打开才可以输入
    if (!cin)
    {
        cin.clear();
        while (cin.get() != '
')
            continue;
    }
    cout << "扩展：
";
    // 2.应用指向数组指针的指针，两种表示方法，pc和pd都是指向同一个数组指针的指针
    auto pc = &pf;
    double (*(*pd)[4])(double x, double y) = &pf;

    while (cin >> x >> y)
    {
        for (int i = 0;i<4;i++)
        {
            //number[i] = calculate(x, y, (*pc)[i]); 
            // 使用pc和pd结果相同，很简单，有定义pc = &pf，那么两边都加上*，*pc = *&pf = pf，和上面一样调用
            // 至于*(*pd)其实和(*pd)效果是一样的，这涉及到了两种学派的使用方法。
            number[i] = calculate(x, y, *(*pd)[i]);
        }
        cout << "加减乘除结果分别为：
";
        for (double i : number)
            cout << i << endl;
        cout << endl;
    }

    return 0;
}

double calculate(double x, double y, double (*pf)(double x, double y))
{
    return pf(x, y);
}

double add(double x, double y)
{
    return x + y;
}

double subtract(double x, double y)
{
    return x - y;
}

double multiply(double x, double y)
{
    return x * y;
}

double divide(double x, double y)
{
    return x / y;
}

运行结果：

2 4
加减乘除结果分别为：
6
-2
8
0.5

q
扩展：
2 4
加减乘除结果分别为：
6
-2
8
0.5

q