overload the operator

运算符重载是c++的又一个先进功能。它使用户可以对自己定义的对象使用运算符像对int、float使用一样方便、简洁、形象，增加程序的可读性。重载运算符既可以用友元函数，也可以用成员函数。推荐使用成员函数进行重载，因为友元函数破坏了c++的封装性。自写程序下：

//overloading operator
#include <iostream.h>

class coor
{
 friend istream &operator>> ( istream &, coor & );
 friend ostream &operator<< ( ostream &, coor & );

public:
 coor( int = 0, int = 0 );
 coor operator+ ( coor & );
 coor operator- ( coor & );
 bool operator== ( coor & );
 bool operator!= ( coor & );

private:
 int x;
 int y;
};

istream &operator>> ( istream &input, coor &d )
{
 input.ignore();
 input >> d.x;
 input.ignore();
 input >> d.y;
 input.ignore();

 return input;
}

ostream &operator<< ( ostream &output, coor &d)
{
 output << '(' << d.x
     << ',' << d.y
     << ')' << endl;

 return output;
}

coor::coor( int X, int Y)
{
 x = X;
 y = Y;
}

coor coor::operator+ ( coor &a )
{
 coor c;
 c.x = this->x + a.x;
 c.y = this->y + a.y;

 return c;
}

coor coor::operator- ( coor &a )
{
 coor c;
 c.x = this->x - a.x;
 c.y = this->y - a.y;

 return c;
}

bool coor::operator== ( coor &a )
{
 if( this->x == a.x && this->y == a.y )
  return true;
 else return false;
}

bool coor::operator!= ( coor &a )
{
 return !( *this == a );
}

int main()
{
 coor num1(5,9), num2(5,9), sum;
 
 cout << "num1 = " << num1 << endl;
 cout << "num2 = " << num2 << endl;
 cout << "sum = " << sum << endl;

 if( num1 == num2 )
  cout << "num1 is equal to num2" << endl;

 if( num1 != num2 )
  cout << "num1 is not equal to num2" << endl;

 cout << "type the num2: " <<endl;
 cin >> num2;
 cout << "num2 = " << num2 <<endl;

 if( num1 == num2 )
  cout << "num1 is equal to num2" << endl;

 if( num1 != num2 )
  cout << "num1 is not equal to num2" << endl;

 sum = num1 + num2;
 cout << "num1 + num2 = sum = " << sum << endl;

 return 0;
}

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