丙加·第9章·答案

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C++版本：

// 50本上限是写给C看的。这里我们使用不限量容器vector（下一章学习）
// 不会也可以模仿后面C的版本创建普通数组。
#include <iostream>
#include <string>
#include <vector>
#include <limits>

using namespace std;

struct Book {
    string name;
    double price;
    long long isbn;
};

void eatline() {
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

int main() {
    vector<Book> books;

    // 50本上限是写给C看的，所以 i < 50 完全可以删掉
    for (int i = 0; i < 50; i++) {
        cout << "-----Book" << (i + 1) << "-----" << endl;

        // 书名
        cout << "Name: ";
        string name;
        getline(cin, name);

        if (name == "%%") {
            cout << endl;
            break;
        }

        // 价格
        double price;
        cout << "Price: ";
        while (!(cin >> price)) {
            cout << "无效的价格，请重新输入: ";
            eatline();
        }

        // ISBN
        long long isbn;
        cout << "ISBN: ";
        while (!(cin >> isbn)) {
            cout << "无效的ISBN，请重新输入: ";
            eatline();
        }
        eatline();

        books.push_back({name, price, isbn});
    }

    // 输出结果
    for (size_t i = 0; i < books.size(); i++) {
        cout << "-----Book" << (i + 1) << "-----" << endl;
        cout << "Name: " << books[i].name << endl;
        cout << "Price: " << books[i].price << endl;
        cout << "ISBN: " << books[i].isbn << endl;
    }

    cout << "\n" << books.size() << " Book(s) in total." << endl;
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX_BOOKS 50
#define MAX_NAME_LENGTH 100

typedef struct {
    char name[MAX_NAME_LENGTH];
    float price;
    long long isbn;
} Book;

// 用于清除缓冲区多余内容
void eatline() {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

int main() {
    Book books[MAX_BOOKS];
    int count = 0;


    for (int i = 0; i < MAX_BOOKS; i++) {
        printf("-----Book%d-----\n", i + 1);

        // 书名
        printf("Name: ");

        // 简单解释下scanf的格式化
        // 空格：  会跳过所有空白字符（包括换行符、空格、制表符等），
        //        避免前一次输入留下的换行符导致本次读取立即结束
        // %99：  限制了最多读取99个字符（留一个给\0）
        // [^\n]：表示读取直到遇到换行符（但不包括换行符）
        if (scanf(" %99[^\n]", books[i].name) != 1) {
            break;
        }

        // 检查结束条件
        if (strcmp(books[i].name, "%%") == 0) {
            printf("\n");
            break;
        }

        // 价格（记得错误检查）
        printf("Price: ");
        while (scanf("%f", &books[i].price) != 1) {
            printf("无效的价格，请重新输入: ");
            eatline();
        }

        // ISBN
        printf("ISBN: ");
        while (scanf("%lld", &books[i].isbn) != 1) {
            printf("无效的ISBN，请重新输入: ");
            eatline();
        }

        count++;

        // 清空输入缓冲区，避免多余的东西跑到下一本书
        // 比如isbn结尾不小心多输入了字母啥的
        eatline(); 
    }

    for (int i = 0; i < count; i++) {
        printf("-----Book%d-----\n", i + 1);
        printf("Name: %s\n", books[i].name);
        printf("Price: %.2f\n", books[i].price);
        printf("ISBN: %lld\n", books[i].isbn);
    }

    printf("\n%d Book(s) in total.\n", count);
    return 0;
}

（接下来的习题只提供 C++版本的答案）

#include <iostream>
#include <limits>
#include <cstring>
#include <cstdio>
#include <cctype>

using namespace std;

const double PI = 3.14159265358;

enum class ShapeType {
    RECT,
    CIRCLE,
};

struct Shape {
    ShapeType type;

    struct {
        int x, y;
    } pos;

    union {
        struct {
            int width, height;
        } rect;
        struct {
            int radius;
        } circle;
    };
};

void eatline() {
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

ShapeType getShapeType();
void enter_shapeInfo(ShapeType type, Shape& shape);
void calc_shapeInfo(const Shape& shape);

int main() {
    ShapeType type = getShapeType();
    Shape shape;

    enter_shapeInfo(type, shape);
    calc_shapeInfo(shape);

    return 0;
}



ShapeType getShapeType() {
    char choice;
    cout << "Shape (R=Rect; C=Circle): ";

    while (true) {
        cin >> choice;
        choice = toupper(choice);

        if (cin.fail() || (choice != 'R' && choice != 'C')) {
            cout << "Error: Invalid shape '" << choice << "'!\n";
            eatline();
            continue;
        }
        break;
    }
    eatline();

    return (choice == 'C') ? ShapeType::CIRCLE : ShapeType::RECT;
}

void enter_shapeInfo(ShapeType type, Shape& shape) {
    shape.type = type;

    cout << "Enter its position: ";
    while (!(cin >> shape.pos.x >> shape.pos.y)) {
        eatline();
        cout << "Error: Invalid position!\n";
    }

    if (type == ShapeType::RECT) {
        cout << "Enter its width and height: ";
        while (!(cin >> shape.rect.width >> shape.rect.height) ||
               shape.rect.width <= 0 || shape.rect.height <= 0) {
            eatline();
            cout << "Error: Invalid width and height! Values must be positive numbers.\n";
        }
    } else {
        cout << "Enter its radius: ";
        while (!(cin >> shape.circle.radius) || shape.circle.radius <= 0) {
            eatline();
            cout << "Error: Invalid radius! Value must be a positive number.\n";
        }
    }
}

void calc_shapeInfo(const Shape& shape) {
    int posx, posy;
    string pointPos;
    double area;

    if (shape.type == ShapeType::CIRCLE) {
        posx = shape.pos.x;
        posy = shape.pos.y + shape.circle.radius;
        pointPos = "at the bottom";
        area = PI * shape.circle.radius * shape.circle.radius;
    } else {
        posx = shape.pos.x + shape.rect.width;
        posy = shape.pos.y + shape.rect.height;
        pointPos = "in the bottom right corner";
        area = shape.rect.height * shape.rect.width;
    }

    printf("Then the coordinates of the point %s are (%d, %d)\n",
           pointPos.c_str(), posx, posy);
    printf("The area of it is %.2lf\n", area);
}

碎碎念：版本答案？

阅读了这么多章节，读者肯定注意到了获取正确输入基本都有一个固定的模式，所以我们完全可以封装起来：

template<typename T>
T get_validInput(const string& prompt, const string& errorMsg) {
 T value;
 cout << prompt;

 while (!(cin >> value)) {
     eatline();
     cout << errorMsg << endl;
 }
 return value;
}

// 在main中使用
char choice = get_validInput<char>(
 "Shape (R=Rect; C=Circle): ",
 "Invalid shape choice!"
);
choice = toupper(choice);

或者利用 C++11 的元组特性，可以输入多个，顺便引入错误检查：

template<typename... Args>
tuple<Args...> get_validInputs(const string& prompt, const string& errorMsg) {
 tuple<Args...> values;
 apply([&](auto&... args) {
     cout << prompt;

     while (!((cin >> ... >> args))) {
         eatline();
         cout << errorMsg << endl;
     }
 }, values);
 return values;
}

// 使用示例：
// 不过需要额外进行负数检查
auto [shape.pos.x, shape.pos.y] = get_validInputs<int, int>("Enter its width and height: ", "Invalid width and height!\n");

这样代码会更简洁些

稍微改造下前面的通用输入函数：

#include <iostream>
#include <cstdio>
#include <ctime>
#include <string>
#include <limits>

using namespace std;

// 清除输入缓冲区
void eatline() {
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

// 通用输入验证模板函数
template<typename T>
T get_validInput(const string& prompt, const string& errorMsg, 
                 bool (*validateFunc)(T) = nullptr) {
    T value;
    while (true) {
        cout << prompt;
        if (cin >> value) {
            // 如果有验证函数，检查值是否有效
            if (validateFunc && !validateFunc(value)) {
                cout << errorMsg << endl;
                eatline();
                continue;
            }
            eatline(); // 清除缓冲区中的换行符
            return value;
        } else {
            eatline();
            cout << errorMsg << endl;
        }
    }
}

// 验证函数 - 检查数据包类型
bool isValidPacketType(char type) {
    return type == 'A' || type == 'a' || type == 'B' || type == 'b';
}

// 打印时间戳的函数
void print_timestamp(long long timestamp) {
    time_t raw_time = (time_t)(timestamp / 1000); // 假设是毫秒时间戳
    struct tm *time_info = localtime(&raw_time);
    printf("%04d-%02d-%02d %02d:%02d:%02d",
           time_info->tm_year + 1900, time_info->tm_mon + 1, time_info->tm_mday,
           time_info->tm_hour, time_info->tm_min, time_info->tm_sec);
}

// 定义数据包类型
enum class PacketType { A, B };

// 使用结构体和联合定义数据包
struct Packet {
    PacketType type;
    union {
        struct {
            int command_code;
            int data_length;
        } typeA;
        struct {
            int status_code;
            long long timestamp;
        } typeB;
    } data;
};

int main() {
    Packet packet;

    // 获取数据包类型（带验证）
    char packetType = get_validInput<char>(
        "Packet Type (A=Command, B=Status): ",
        "Error: Invalid packet type! Please enter A or B.",
        isValidPacketType
        );

    if (packetType == 'A' || packetType == 'a') {
        packet.type = PacketType::A;

        // 获取命令码
        // 使用scanf的理由是
        // 可以一次性处理八、十、十六进制各种格式的输入
        // 八进制： 0100   -> 64
        // 十进制：  100   -> 100
        // 十六进制：0x100 -> 256
        cout << "Enter command code: ";
        while (true) {
            if (scanf("%i", &packet.data.typeA.command_code) == 1) {
                eatline();
                break;
            } else {
                eatline(); // 清除错误输入
                cout << "Error: Invalid command code format! Please enter a valid integer: ";
            }
        }

        // 获取数据长度（带验证）
        // 注意前后类型匹配：<int> 和 [](int v)
        packet.data.typeA.data_length = get_validInput<int>(
            "Enter data length: ",
            "Error: Data length must be a positive integer!",
            [](int v) { return v > 0; }
            );

        cout << "--- Packet A Info ---" << endl;
        // 这里hex是std::hex控制符
        cout << "Command: 0x" << hex << uppercase << packet.data.typeA.command_code << endl;
        cout << "Data Length: " << dec << packet.data.typeA.data_length << " bytes" << endl;
    }
    else if (packetType == 'B' || packetType == 'b') {
        packet.type = PacketType::B;

        // 获取状态码
        packet.data.typeB.status_code = get_validInput<int>(
            "Enter status code: ",
            "Error: Status code must be a positive integer!",
            [](int v) { return v > 0; }
            );

        // 获取时间戳
        packet.data.typeB.timestamp = get_validInput<long long>(
            "Enter timestamp: ",
            "Error: Timestamp must be a non-negative integer!",
            [](long long int v) { return v >= 0; }
            );

        cout << "--- Packet B Info ---" << endl;
        cout << "Status: " << packet.data.typeB.status_code << endl;
        cout << "Timestamp: ";
        print_timestamp(packet.data.typeB.timestamp);
        cout << endl;
    }

    return 0;
}

修改 calc_shapeInfo 即可：

void calc_shapeInfo(const Shape& shape) {
    int posx, posy;
    string pointPos;
    double area;

    // 放大后的变量
    int resized_posx, resized_posy;
    double resized_area;

    if (shape.type == ShapeType::CIRCLE) {
        posx = shape.pos.x;
        posy = shape.pos.y + shape.circle.radius;
        pointPos = "at the bottom";
        area = PI * shape.circle.radius * shape.circle.radius;

        // 放大2倍后的计算
        resized_posx = shape.pos.x;
        resized_posy = shape.pos.y + shape.circle.radius * 2;
        resized_area = PI * shape.circle.radius * 2 * shape.circle.radius * 2;
    } else {
        posx = shape.pos.x + shape.rect.width;
        posy = shape.pos.y + shape.rect.height;
        pointPos = "in the bottom right corner";
        area = shape.rect.height * shape.rect.width;

        // 放大2倍后的计算
        resized_posx = shape.pos.x + shape.rect.width * 2;
        resized_posy = shape.pos.y + shape.rect.height * 2;
        resized_area = shape.rect.height * 2 * shape.rect.width * 2;
    }

    printf("Then the coordinates of the point %s are (%d, %d)\n",
           pointPos.c_str(), posx, posy);
    printf("The area of it is %.0lf\n", area);

    // 添加放大后的输出
    printf("If resized to 2x:\n");
    printf("Then the coordinates of the point %s are (%d, %d)\n",
           pointPos.c_str(), resized_posx, resized_posy);
    printf("The area of it is %.0lf\n", resized_area);
}

作者

命令提示符@CommandPrompt-Wang