C++和标准库速成(十二)——练习

练习1.1

题目

  修改下面的Employee结构体，将其放在一个名为HR的名称空间中。你必须对main()中的代码进行那些修改才能使用此新实现？此外，修改代码使用C++20的指派初始化器。

// employee模块接口文件
export module employee;export struct Employee {char firstInitial;char lastInitial;int employeeNumber;int salary;
};

// main
// import <iostream>;
// import <format>;
import std.core;
import employee;int main() {Employee anEmployee;anEmployee.firstInitial = 'J';anEmployee.lastInitial = 'D';anEmployee.employeeNumber = 42;anEmployee.salary = 80'000;std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastinitial);std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);std::cout << std::format("Salary: ${}\n", anEmployee.salary);
}

答案

// employee模块接口文件
export module employee;namespace HR {export struct Employee {char firstInitial;char lastInitial;int employeeNumber;int salary;};
}

// main()
import std.core;
import employee;int main() {HR::Employee anEmployee{.firstInitial = 'J',.lastInitial = 'D',.employeeNumber = 42,.salary = 80'000};std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastInitial);std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);std::cout << std::format("Salary: {}\n", anEmployee.salary);
}

练习1.2

题目

  以练习1.1的结果为基础，并向Employee添加一个枚举数据成员title，以指定某个雇员是经理，高级工程师还是工程师。你将选用哪种枚举类型？无论需要添加什么，都将其添加到HR名称空间中。在main()函数中测试新的Employee数据成员。使用switch语句为title打印出易于理解的字符串。

答案

// employee模块接口文件
export module employee;namespace HR {export enum class position {MANAGER,ENGINEER,SENIOR_ENGINEER};export struct Employee {char firstInitial;char lastInitial;int employeeNumber;int salary;position title;};
}

// main()
import std.core;
import employee;int main() {std::string title;HR::Employee anEmployee{.firstInitial = 'J',.lastInitial = 'D',.employeeNumber = 42,.salary = 80'000,.title = HR::position::ENGINEER};std::cout << std::format("Employee: {}{}\n", anEmployee.firstInitial, anEmployee.lastInitial);std::cout << std::format("Number: {}\n", anEmployee.employeeNumber);std::cout << std::format("Salary: {}\n", anEmployee.salary);switch (anEmployee.title) {case HR::position::ENGINEER:title = "Engineer";break;case HR::position::MANAGER:title = "Manager";break;case HR::position::SENIOR_ENGINEER:title = "Senior Engineer";break;}if (!title.empty()) {std::cout << std::format("Title: {}\n", title);}
}

练习1.3

题目

  使用std::array存储练习1.2中具有不同数据的3个Employee实例，然后使用基于范围的for循环打印出array中的雇员。

答案

// main()
import std.core;
import employee;static const std::string title(HR::position pos) {std::string title;switch (pos) {case HR::position::ENGINEER:title = "Engineer";break;case HR::position::MANAGER:title = "Manager";break;case HR::position::SENIOR_ENGINEER:title = "Senior Engineer";break;}return title;
}static void display(HR::Employee employee) {std::cout << std::format("Employee: {} {}\n", employee.firstInitial, employee.lastInitial);std::cout << std::format("Number: {}\n", employee.employeeNumber);std::cout << std::format("Salary: {}\n", employee.salary);std::cout << std::format("Title: {}\n\n", title(employee.title));
}int main() {std::array<HR::Employee, 3> employees{ {{'J', 'D', 42, 80'000, HR::position::MANAGER },{'A', 'H', 43, 60'000, HR::position::SENIOR_ENGINEER },{'C', 'B', 44, 40'000, HR::position::ENGINEER }}};for (auto& employee : employees) {display(employee);}
}

练习1.4

题目

  进行与练习1.3相同的操作，但使用std::vector而不是array，并使用push_back()将元素插入vector中。

答案

// main()
import std.core;
import employee;static const std::string title(HR::position pos) {std::string title;switch (pos) {case HR::position::ENGINEER:title = "Engineer";break;case HR::position::MANAGER:title = "Manager";break;case HR::position::SENIOR_ENGINEER:title = "Senior Engineer";break;}return title;
}static void display(HR::Employee employee) {std::cout << std::format("Employee: {} {}\n", employee.firstInitial, employee.lastInitial);std::cout << std::format("Number: {}\n", employee.employeeNumber);std::cout << std::format("Salary: {}\n", employee.salary);std::cout << std::format("Title: {}\n\n", title(employee.title));
}int main() {HR::Employee employee1 { 'J', 'D', 42, 80'000, HR::position::MANAGER };HR::Employee employee2 { 'A', 'H', 43, 60'000, HR::position::SENIOR_ENGINEER };HR::Employee employee3 { 'C', 'B', 44, 40'000, HR::position::ENGINEER };std::vector<HR::Employee> employees;employees.push_back(employee1);employees.push_back(employee2);employees.push_back(employee3);for ( auto& employee : employees ) {display(employee);}
}

练习1.5

题目

  修改下面的AirlineTicket类，以尽可能地使用引用，并正确使用const。

// airline_ticket模块接口文件
export module airline_ticket;// import <string>;
import std.core; // MSVCexport class AirlineTicket {
public:AirlineTicket(); // constructor~AirlineTicket(); // destructordouble calculatePriceInDollars();std::string getPassengerName();void setPassengerName(std::string name);int getNumberOfMiles();void setNumberOfMiles(int miles);bool hasEliteSuperRewardsStatus();void setHasEliteSuperRewardsStatus(bool status);private:std::string m_passengerName;int m_numberOfMiles;bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;AirlineTicket::AirlineTicket() :m_passengerName{ "Unknown Passenger" },m_numberOfMiles{ 0 },m_hasEliteSuperRewardsStatus{ false } {
}AirlineTicket::~AirlineTicket() {// nothong to do in terms of cleanup.
}double AirlineTicket::calculatePriceInDollars() {if (hasEliteSuperRewardsStatus()) {// elite super rewards customers fly for free!return 0;}// the cost of the ticket is  the number of milies times 0.1.// real airlines probably have a more complicated formula!return getNumberOfMiles() * 0.1;
}std::string AirlineTicket::getPassengerName() {return m_passengerName;
}void AirlineTicket::setPassengerName(std::string name) {m_passengerName = name;
}int AirlineTicket::getNumberOfMiles() {return m_numberOfMiles;
}void AirlineTicket::setNumberOfMiles(int miles) {m_numberOfMiles = miles;
}bool AirlineTicket::hasEliteSuperRewardsStatus() {return m_hasEliteSuperRewardsStatus;
}void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {m_hasEliteSuperRewardsStatus = status;
}

答案

// airline_ticket模块接口文件
export module airline_ticket;// import <string>;
import std.core; // MSVCexport class AirlineTicket {
public:AirlineTicket(); // constructor~AirlineTicket(); // destructordouble calculatePriceInDollars() const;const std::string& getPassengerName() const;void setPassengerName(const std::string& name);int getNumberOfMiles() const;void setNumberOfMiles(int miles);bool hasEliteSuperRewardsStatus() const;void setHasEliteSuperRewardsStatus(bool status);private:std::string m_passengerName;int m_numberOfMiles;bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;AirlineTicket::AirlineTicket() :m_passengerName{ "Unknown Passenger" },m_numberOfMiles{ 0 },m_hasEliteSuperRewardsStatus{ false } {
}AirlineTicket::~AirlineTicket() {// nothong to do in terms of cleanup.
}double AirlineTicket::calculatePriceInDollars() const {if (hasEliteSuperRewardsStatus()) {// elite super rewards customers fly for free!return 0;}// the cost of the ticket is  the number of milies times 0.1.// real airlines probably have a more complicated formula!return getNumberOfMiles() * 0.1;
}const std::string& AirlineTicket::getPassengerName() const {return m_passengerName;
}void AirlineTicket::setPassengerName(const std::string& name) {m_passengerName = name;
}int AirlineTicket::getNumberOfMiles() const {return m_numberOfMiles;
}void AirlineTicket::setNumberOfMiles(int miles) {m_numberOfMiles = miles;
}bool AirlineTicket::hasEliteSuperRewardsStatus() const {return m_hasEliteSuperRewardsStatus;
}void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {m_hasEliteSuperRewardsStatus = status;
}

练习1.6

题目

  修改练习1.5中的AirlineTicket类，使其包含一个可选的常旅客号码。表示此可选数据成员的最佳方法是什么？添加一个设置器和获取器来设置和获取常旅客号码。修改main()函数以测试你的实现。

答案

// airline_ticket模块接口文件
export module airline_ticket;// import <string>;
import std.core; // MSVCexport class AirlineTicket {
public:AirlineTicket(); // constructor~AirlineTicket(); // destructordouble calculatePriceInDollars();std::string getPassengerName();void setPassengerName(std::string name);int getNumberOfMiles();void setNumberOfMiles(int miles);void setFrequentFlyerNumber(int frequentFlyerNumber);std::optional<int> getFrequentFlyerNumber() const;bool hasEliteSuperRewardsStatus();void setHasEliteSuperRewardsStatus(bool status);private:std::string m_passengerName;int m_numberOfMiles;std::optional<int> m_frequentFlyerNumber;bool m_hasEliteSuperRewardsStatus;
};

// airline_ticket模块实现文件
module airline_ticket;AirlineTicket::AirlineTicket() :m_passengerName{ "Unknown Passenger" },m_numberOfMiles{ 0 },m_hasEliteSuperRewardsStatus{ false } {
}AirlineTicket::~AirlineTicket() {// nothong to do in terms of cleanup.
}double AirlineTicket::calculatePriceInDollars() {if (hasEliteSuperRewardsStatus()) {// elite super rewards customers fly for free!return 0;}// the cost of the ticket is  the number of milies times 0.1.// real airlines probably have a more complicated formula!return getNumberOfMiles() * 0.1;
}std::string AirlineTicket::getPassengerName() {return m_passengerName;
}void AirlineTicket::setPassengerName(std::string name) {m_passengerName = name;
}int AirlineTicket::getNumberOfMiles() {return m_numberOfMiles;
}void AirlineTicket::setNumberOfMiles(int miles) {m_numberOfMiles = miles;
}void AirlineTicket::setFrequentFlyerNumber(int frequentFlyerNumber) {m_frequentFlyerNumber = frequentFlyerNumber;
}
std::optional<int> AirlineTicket::getFrequentFlyerNumber() const {return m_frequentFlyerNumber;
}bool AirlineTicket::hasEliteSuperRewardsStatus() {return m_hasEliteSuperRewardsStatus;
}void AirlineTicket::setHasEliteSuperRewardsStatus(bool status) {m_hasEliteSuperRewardsStatus = status;
}

// main()
import std.core;
import airline_ticket;int main() {AirlineTicket myTicket;myTicket.setPassengerName("Sherman T. Socketwrench");myTicket.setNumberOfMiles(700);myTicket.setFrequentFlyerNumber(123'456);const double cost{ myTicket.calculatePriceInDollars() };std::cout << std::format("This ticket will cost ${}\n", cost);const auto frequentFlyerNumber{ myTicket.getFrequentFlyerNumber() };if (frequentFlyerNumber) {std::cout << std::format("Frequent flyer number: {}\n", frequentFlyerNumber.value());}else {std::cout << "No frequent flyer number.\n";}
}

参考

[比] 马克·格雷戈勒著 程序喵大人 惠惠 墨梵 译 C++20高级编程(第五版)