當一天設置為當月的第一天並減少時，如何解決這個問題，它應該成為上個月的最后一天？

Question

這是我第一次嘗試這樣的問題。解決這個問題對我來說非常困難，因為由於某些原因，我在教授這個問題時無法上課。誰能幫助我如何使用遞減運算符作為我不知道在哪里以及如何添加此類運算符以獲得理想的輸出。 我已經遲到了兩天提交這個作業:(

#include <iostream>
using namespace std;

class Date{
   private:
      int day;
      int month;
      int year;

   public:
   Date()
   {
        day;
        month;
        year;
   }
      Date(int d, int m , int y)
      {
         day = d;
       month = m;
        year = y;
      }
       void displayDate() {
         cout << "Day: " << day << " Month:" << month <<" Year:"<<year<<endl;
      }
// overloaded prefix ++ operator
      Date operator++ () {
         ++day;
         ++year;
         ++month;

         if(day >= 31) {

            day -= 31;
         }
        if (month>=12)
        {
         month -= 12;
         }
         return Date(day, month,year);
      }
      };




int main ()
{
      int day;
      int month;
      int year;
      string month_name[20] = {"January","February","March","April","May","June","July","August","September","October","November","December"};

     do{
      cout << "Enter a day: ";
      cin >> day;

         if (day > 31 || day < 1)
         cout<<"This is invalid "<<endl;
        }

     while (day > 31 || day < 1);

     do{
      cout << "Enter a month: " ;
      cin >> month;

         if (month > 12 || month < 1)
         cout<<"This is invalid "<<endl;
       }

     while (month > 12 || month < 1);
      cout << "Enter a year: ";
     cin >> year;


    cout << month << "/" << day << "/" << year << endl;
    cout << month_name[month-1]<< " " << day << ", " << year << endl;
    cout << day << " " <<  month_name[month-1] << "," << year << endl;



   Date D1(day,month,year);
   ++D1;            // increment D1
   D1.displayDate();   // display D1
   ++D1;               // increment of D1 again
   D1.displayDate();        // display D1

   return 0;

}

Answer 1

您基本上可以使用增量運算符執行相同的操作，但可以向后執行。 用於遞減的 C++ 運算符是--variable ，因此代碼如下所示

Date operator--(){
    --day;
    --year;
    --month;
    if(day <= 0) 
    {
        day += 31;
    }
    if (month<=0)
    {
        month += 12;
    }
    return Date(day, month,year);
}