// constructor/destructor
// copy constructor  vs.  assigment operator=()
// member operator/function  vs.  friend operator/function
//////////////////////////////////////////////////////////
#include <iostream.h>
class INT{
      long val_;
   public:
      INT(){ val_= -999; cout << ":hi.."; }
      INT(long n){ val_ = n; cout << ":ha.."<<val_; }
      INT(const INT& k){ val_ = k.val_; cout << "(copy "<<val_<<")"; }
      friend ostream& operator<<(ostream&,const INT&);
      //friend ostream& operator<<(ostream&,const INT);
      ~INT(){ cout << " ["<< val_ << " is dying...\n"; }
      INT& operator+(const INT&n); //注意"+"和"*"用不同寫法:member vs friend
      INT  friend operator*(const INT&, const INT&);  // 注意參數
      INT& operator=(const INT&n)
  //overload assignment function INT::operator=(INT&n)
      {  this->val_ = 100* n.val_;
         cout << "(="<<val_<<")";
         return *this;
      }
};
extern INT x;      // 這只是宣告
INT y(5252);       // declare + define
int main(){
   INT a, b(38) ;  // "hi.." for a,   "ha.." for b
   cout << endl << "- - -" << endl;
   cout << "a=" << a << endl; cout << "b=" << b << endl;
    INT c(b);     // invoke copy construtor to construct c
    INT d = c;    // same as above, this invokes copy construtor too
      INT e;  e=b;  // invoke assignment function (operator=)
   cout << endl << "------" << endl;
   cout << "c=" << c << endl; cout << "d=" << d << endl;
   cout << "e=" << e << endl;
   cout << "x=" << x << endl; cout << "y=" << y << endl;
   cout << "== now do x=250; ==\n";
   x=250;
   cout << "x=" << x << endl;
   cout << "== now do c= e + d; == Note 加的結果\n";
   c = e + d;
   cout << "c=" << c << endl;
   cout << "d=" << d << endl;
   cout << "== now do d= d + 25; == Did we define operator+(INT&, int) ?\n";
   cout << "== actually, 'cast' will happen. (INT)25 invokes INT(25)\n";
   d = d + 25;
   cout << "d=" << d << endl;
   cout << "== Now output e  ==\n";
   cout << "e=" << e << endl;
   cout << "== Now output  d*e == Note * 的結果\n";
   cout << "d*e= " << d*e <<endl;
   cout << "x=" << x << endl; cout << "y=" << y << endl;
   cout << "=== bye bye 最先生的最慢死 ===\n";
   cout << "=== y x a b c d e ... e d c b a x y ===\n";
}
INT x(49);
ostream& operator<<(ostream& out, const INT&n)
{
  out << n.val_; 
  return out;
}
  //overload assignment function INT::operator+(INT&n)
INT& INT::operator+(const INT&n)
{  val_ = this->val_ -  n.val_;
   /// Note that this "+" has side effect !
   ////////////////////////////////////////
   cout<<"(addition done:"<<val_<<")";
   return *this;
}
INT operator*(const INT&a, const INT&b)
{ INT tmp;
  cout << "(doing *)";
  tmp.val_ = a.val_ & b.val_;  // bit-wise and
  cout << "(* done)";
  return tmp;
}