overload the >> operator in c++

class Point
{
public:
	Point& operator++() { ... }		// prefix
	Point operator++(int) { ... }	// postfix
  	friend Point& operator++(Point &p);			// friend prefix
  	friend Point operator++(Point &p, int);		// friend postfix
  	// in Microsoft Docs written "friend Point& operator++(Point &p, int);"
};

#include <iostream> 
using namespace std; 
  
class Complex 
{ 
private: 
    int real, imag; 
public: 
    Complex(int r = 0, int i =0) 
    {  real = r;   imag = i; } 
    friend ostream & operator << (ostream &out, const Complex &c); 
    friend istream & operator >> (istream &in,  Complex &c); 
}; 
  
ostream & operator << (ostream &out, const Complex &c) 
{ 
    out << c.real; 
    out << "+i" << c.imag << endl; 
    return out; 
} 
  
istream & operator >> (istream &in,  Complex &c) 
{ 
    cout << "Enter Real Part "; 
    in >> c.real; 
    cout << "Enter Imaginary Part "; 
    in >> c.imag; 
    return in; 
} 
  
int main() 
{ 
   Complex c1; 
   cin >> c1; 
   cout << "The complex object is "; 
   cout << c1; 
   return 0; 
}

#include <iostream>
using namespace std;

class Box {
   public:
      double getVolume(void) {
         return length * breadth * height;
      }
      void setLength( double len ) {
         length = len;
      }
      void setBreadth( double bre ) {
         breadth = bre;
      }
      void setHeight( double hei ) {
         height = hei;
      }
      
      // Overload + operator to add two Box objects.
      Box operator+(const Box& b) {
         Box box;
         box.length = this->length + b.length;
         box.breadth = this->breadth + b.breadth;
         box.height = this->height + b.height;
         return box;
      }
      
   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

// Main function for the program
int main() {
   Box Box1;                // Declare Box1 of type Box
   Box Box2;                // Declare Box2 of type Box
   Box Box3;                // Declare Box3 of type Box
   double volume = 0.0;     // Store the volume of a box here
 
   // box 1 specification
   Box1.setLength(6.0); 
   Box1.setBreadth(7.0); 
   Box1.setHeight(5.0);
 
   // box 2 specification
   Box2.setLength(12.0); 
   Box2.setBreadth(13.0); 
   Box2.setHeight(10.0);
 
   // volume of box 1
   volume = Box1.getVolume();
   cout << "Volume of Box1 : " << volume <<endl;
 
   // volume of box 2
   volume = Box2.getVolume();
   cout << "Volume of Box2 : " << volume <<endl;

   // Add two object as follows:
   Box3 = Box1 + Box2;

   // volume of box 3
   volume = Box3.getVolume();
   cout << "Volume of Box3 : " << volume <<endl;

   return 0;
}

istream &operator>>( istream  &input, Class_Name &c )