C++ ++ and -- Operator Overloading

C++ Operator Overloading and Overloaded Functions

The increment operator (++) and decrement operator (--) are two important unary operators in the C++ language.

The following example demonstrates how to overload the increment operator (++), including both prefix and postfix usages. Similarly, you can also try to overload the decrement operator (--).

Example

#include <iostream>
using namespace std;

class Time
{
   private:
      int hours;             // 0 to 23
      int minutes;           // 0 to 59
   public:
      // Required constructor
      Time(){
         hours = 0;
         minutes = 0;
      }
      Time(int h, int m){
         hours = h;
         minutes = m;
      }
      // Method to display time
      void displayTime()
      {
         cout << "H: " << hours << " M:" << minutes <&lt;endl;
      }
      // Overload prefix increment operator (++)
      Time operator++ ()  
      {
         ++minutes;          // Increment the object
         if(minutes >= 60)  
         {
            ++hours;
            minutes -= 60;
         }
         return Time(hours, minutes);
      }
      // Overload postfix increment operator (++)
      Time operator++( int )         
      {
         // Save the original value
         Time T(hours, minutes);
         // Increment the object
         ++minutes;                    
         if(minutes >= 60)
         {
            ++hours;
            minutes -= 60;
         }
         // Return the old original value
         return T; 
      }
};
int main()
{
   Time T1(11, 59), T2(10,40);

   ++T1;                    // Increment T1
   T1.displayTime();        // Display T1
   ++T1;                    // Increment T1 again
   T1.displayTime();        // Display T1

   T2++;                    // Increment T2
   T2.displayTime();        // Display T2
   T2++;                    // Increment T2 again
   T2.displayTime();        // Display T2
   return 0;
}

When the above code is compiled and executed, it produces the following result:

H: 12 M:0
H: 12 M:1
H: 10 M:41
H: 10 M:42

Note that int inside the parentheses is to inform the compiler that this is a postfix form, not an integer.

The prefix form overload calls Check operator ++ (), and the postfix form overload calls operator ++ (int).

Example (++ Overloading)

#include <iostream>
using namespace std;

class Check
{
  private:
    int i;
  public:
    Check(): i(0) {  }
    Check operator ++ ()
    {
        Check temp;
        temp.i = ++i;
        return temp;
    }

    // Inserting int in parentheses indicates postfix
    Check operator ++ (int)
    {
        Check temp;
        temp.i = i++;
        return temp;
    }

    void Display()

#include <iostream>
using namespace std;

class Check
{
  private:
    int i;
  public:
    Check(): i(0) {  }
    Check operator ++ ()
    {
        Check temp;
        temp.i = ++i;
        return temp;
    }

    // Postfix form
    Check operator ++ (int)
    {
        Check temp;
        temp.i = i++;
        return temp;
    }

    void Display()
    { cout << "i = " << i << endl; }
};

int main()
{
    Check obj, obj1;    
    obj.Display(); 
    obj1.Display();

    // Call the operator function and then assign obj's value to obj1
    obj1 = ++obj;
    obj.Display();
    obj1.Display();

    // Assign obj to obj1, then call the operator function
    obj1 = obj++;
    obj.Display();
    obj1.Display();

    return 0;
}

Execution output:

i = 0
i = 0
i = 1
i = 1
i = 2
i = 1

Example (-- Overloading)

#include <iostream>
using namespace std;

class Check
{
  private:
    int i;
  public:
    Check(): i(3) {  }
    Check operator -- ()
    {
        Check temp;
        temp.i = --i;
        return temp;
    }

    // Insert int in parentheses to indicate postfix
    Check operator -- (int)
    {
        Check temp;
        temp.i = i--;
        return temp;
    }

    void Display()
    { cout << "i = " << i << endl; }
};

int main()
{
    Check obj, obj1;    
    obj.Display(); 
    obj1.Display();

    // Call the operator function and then assign obj's value to obj1
    obj1 = --obj;
    obj.Display();
    obj1.Display();

    // Assign obj to obj1, then call the operator function
    obj1 = obj--;
    obj.Display();
    obj1.Display();

    return 0;
}

Execution output:

i = 3
i = 3
i = 2
i = 2
i = 1
i = 2

C++ Overloading Operators and Functions ```