星期二+ 3 =星期五？ C++编程问题

Question

看看主函数，我们可以看到我已经将“星期一”硬编码到了我的setDay公共函数中。从用户使用c字符串（正如我在setDay中那样）获取一周中的某一天很容易，但是如何让用户将n添加到设置的日期“星期一”并提出“星期四”？因为typdef枚举{INVALID，周一，周二，周三，周四，周五，周六，周日}不解释图9是0和/或10如1

#include <iostream> 

using std::cout; 
using std::endl; 

class DayOfTheWeek //class is encapsulation of functions and members that manipulate the data. 
{ 
public: 

DayOfTheWeek(); // Constructor 
virtual ~DayOfTheWeek(); // Destructor 

void setDay(const char * day); // Function to set the day 
void printDay() const;  // Function to Print the day. 
const char * getDay() const; // Function to get the day. 

const char * plusOneDay(); // Next day function 
const char * minusOneDay(); // Previous day function 
const char * addDays(int addValue); // function that adds days based on parameter value 

private: 
char * day; // variable for the days of the week. 

}; 

DayOfTheWeek::DayOfTheWeek() : day(0) 
{ 
// Usually I would allocate pointer member variables 
// Here in the construction of the Object 
} 

const char * DayOfTheWeek::getDay() const 
{ 
return day; // we can get the day simply by returning it. 
} 

const char * DayOfTheWeek::minusOneDay() 
{ 
if (strcmp(day, "Monday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Sunday"; 
} 
else if (strcmp(day, "Tuesday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Monday"; 
} 
else if (strcmp(day, "Wednesday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Tuesday"; 
} 
else if (strcmp(day, "Thursday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Wednesday"; 
} 
else if (strcmp(day, "Friday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Thursday"; 
} 
else if (strcmp(day, "Saturday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Friday"; 
} 
else if (strcmp(day, "Sunday") == 0) 
{ 
    cout << "The day before " << day << " is "; 
    return "Saturday"; 
} 
else 
{ 
    cout << "'" << day << "'"; 
    return "is an invalid day of the week!"; 
} 
} 

const char * DayOfTheWeek::plusOneDay() 
{ 
if (strcmp(day, "Monday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Tuesday"; 
} 
else if (strcmp(day, "Tuesday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Wednesday"; 
} 
else if (strcmp(day, "Wednesday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Thursday"; 
} 
else if (strcmp(day, "Thursday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Friday"; 
} 
else if (strcmp(day, "Friday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Saturday"; 
} 
else if (strcmp(day, "Saturday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Sunday"; 
} 
else if (strcmp(day, "Sunday") == 0) 
{ 
    cout << "The day after " << day << " is "; 
    return "Monday"; 
} 
else 
{ 
    cout << "'" << day << "'"; 
    return " is an invalid day of the week!"; 
} 
} 

const char * DayOfTheWeek::addDays(int addValue) 
{ 
if (addValue < 0) 
{ 
    if (strcmp(day, "Monday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Friday"; 
    } 
    else if (strcmp(day, "Tuesday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Saturday"; 
    } 
    else if (strcmp(day, "Wednesday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Sunday"; 
    } 
    else if (strcmp(day, "Thursday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Monday"; 
    } 
    else if (strcmp(day, "Friday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Tuesday"; 
    } 
    else if (strcmp(day, "Saturday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Wednesday"; 
    } 
    else if (strcmp(day, "Sunday") == 0) 
    { 
    cout << day << " - " << -addValue << " = "; 
    return "Thursday"; 
    } 
    else 
    { 
    cout << "'" << day << "' "; 
    return "is an invalid day of the week! "; 
    } 
} 
else // if our parameter is greater than 0 (positive) 
{ 
    if (strcmp(day, "Monday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Thursday"; 
    } 
    else if (strcmp(day, "Tuesday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Friday"; 
    } 
    else if (strcmp(day, "Wednesday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Saturday"; 
    } 
    else if (strcmp(day, "Thursday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Sunday"; 
    } 
    else if (strcmp(day, "Friday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Monday"; 
    } 
    else if (strcmp(day, "Saturday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Tuesday"; 
    } 
    else if (strcmp(day, "Sunday") == 0) 
    { 
    cout << day << " + " << addValue << " = "; 
    return "Wednesday"; 
    } 
    else 
    { 
    cout << "'" << day << "' "; 
    return "is an invalid day of the week! "; 
    } 
} 
} 

void DayOfTheWeek::printDay() const 
{ 
cout << "The Value of the " << day; 
} 

void DayOfTheWeek::setDay(const char * day) 
{ 
if (day) 
{// Here I am allocating the object member char day pointer 
    this->day = new char[strlen(day)+1]; 
    size_t length = strlen(day)+1; // +1 for trailing null char 
    strcpy_s(this->day , length , day); // copying c-strings 
} 
else day = NULL; // If their was a problem with the parameter 'day' 
} 

DayOfTheWeek::~DayOfTheWeek() 
{ 
delete day; // Free the memory allocated in SetDay 
} 

int main() 
{ 
DayOfTheWeek MondayObject; // declare an object 

MondayObject.setDay("Monday"); // Call our public function 'setDay' to set a day of the week 
MondayObject.printDay();  // Call our public function 'printDay' to print the day we set 

cout << " object is " << MondayObject.getDay() << endl; // Print the value of the object 

cout << MondayObject.plusOneDay() << endl; 
cout << MondayObject.minusOneDay() << endl; 
cout << MondayObject.addDays(3) << endl; 

    MondayObject.printDay(); 
cout << " object is still " << MondayObject.getDay() << endl; // Print the value of the object 

cout << MondayObject.addDays(-3) << endl; 

return 0; 
} 

Answer 1

而不是试图使用字符串这是很难要存储它的哪一天，你可能只想在类中使用一个整数来存储星期几。整数和模数算术最常用于存储这类数据。

如果您存储星期几到星期一的星期几为0到6，则可以使用模运算符%对其进行简单的操作;任何时候你不知道一个操作是否在这个范围内，你可以做

nDay = nDay % 7; 

它会达到你期望的值;如果它已经从6上升到9，例如，它会回来环绕于2

Answer 2

您可以使用枚举和封装周日，周一侧翻：

enum Weekday { 
    INVALID, 
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY 
}; 
Weekday operator+(Weekday w, int n) { 
    if (w == INVALID) return w; 
    n %= 7; 
    if (n < 0) n += 7; 
    return Weekday((n + (w - 1)) % 7 + 1); 
} 
Weekday operator+(int n, Weekday w) { return w + n; } 
Weekday operator-(Weekday w, int n) { return w + -n; } 
Weekday operator-(int n, Weekday w); // not defined -- doesn't make sense and not 
// to be used 

std::string str(Weekday d) { 
    assert(INVALID <= d && d <= SUNDAY); // function precondition 
    static char const* const days[] = { 
    "INVALID", 
    "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY", "SATURDAY", "SUNDAY" 
    }; 
    return days[d]; 
} 

// you would probably not call this directly, but it shows how you simply have to 
// pick what day int(0) means, and add any int to that day to get a Weekday 
Weekday Weekday_from_num(int n, Weekday zero=MONDAY) { 
    return zero + n; 
} 

Test：

int main() { 
    assert(MONDAY + 1 == TUESDAY); 
    assert(MONDAY + 8 == TUESDAY); 
    assert(MONDAY - 1 == SUNDAY); 
    assert(MONDAY - 8 == SUNDAY); 

    cout << "MONDAY + 3 is " << str(MONDAY + 3) << '\n'; 
    return 0; 
} 

但是，我会放弃无效（这也简化了数学）。你已经写了一个Weekday_from_str函数，你只需要调整它就可以返回这个枚举。

Answer 3

这种（经常碰到）问题并不需要写一个类，包含枚举和两个函数的命名空间是不够的：

#include <iostream> 
namespace day { 

enum e_DAY { Sun, Mon, Tue, Wed, Thu, Fri, Sat }; 

inline e_DAY GetDay(unsigned int i) 
{ 
    return (e_DAY)(i % 7); 
} 

inline const wchar_t* GetName(unsigned int i) 
{ 
    static wchar_t* Names[] = { L"Sunday", L"Monday", L"Tuesday", L"Wednesday", L"Thursday", L"Friday", L"Saturday" }; 
    return Names[GetDay(i)]; 
} 

} // namespace day 

int main(int argc, wchar_t* argv[]) 
{    
    std::wcout << day::Tue + 3 << "\t" << day::GetName(day::Tue + 3) << std::endl; 
    return 0; 
}