c++ - 星期二 + 3 = 星期五？ C++编程问题

Question

查看 main 函数，我们可以看到我已将“星期一”硬编码到我的 setDay 公共(public)函数中。使用 c 字符串很容易从用户那里获取星期几(就像我在 setDay 中所做的那样)，但是我如何要求用户将 n 添加到设置的日期“星期一”并提出“周四”？这很难，因为 typdef enum { INVALID, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY} 不会将 9 解释为 0 和/或 10 为 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

与其尝试使用字符串来存储星期几，您可能只想在类中使用整数来存储星期几。整数和模数运算最常用于存储此类数据。

如果您将星期几存储为星期日到星期一是 0 到 6，您可以使用模数运算符 % 对其进行简单的操作；任何时候你不知道一个操作是否在那个范围内，你可以做

nDay = nDay % 7;

它会达到您期望的值；例如，如果它从 6 上升到 9，它将回到 2。