4.Object Oriented Programming

The codes:

// 4.Object Oriented Programming

/*********************************************************
1
Classes (I)
*/

// classes example
#include <iostream>
using namespace std;

class CRectangle {
    int x, y;
  public:
    void set_values (int,int);
    int area () {return (x*y);}
};

void CRectangle::set_values (int a, int b) {
  x = a;
  y = b;
}

int main () {
  CRectangle rect;
  rect.set_values (3,4);
  cout << "area: " << rect.area();
  return 0;
}


// example: one class, two objects
#include <iostream>
using namespace std;

class CRectangle {
    int x, y;
  public:
    void set_values (int,int);
    int area () {return (x*y);}
};

void CRectangle::set_values (int a, int b) {
  x = a;
  y = b;
}

int main () {
  CRectangle rect, rectb;
  rect.set_values (3,4);
  rectb.set_values (5,6);
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}


// example: class constructor
#include <iostream>
using namespace std;

class CRectangle {
    int width, height;
  public:
    CRectangle (int,int);
    int area () {return (width*height);}
};

CRectangle::CRectangle (int a, int b) {
  width = a;
  height = b;
}

int main () {
  CRectangle rect (3,4);
  CRectangle rectb (5,6);
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}



// example on constructors and destructors
#include <iostream>
using namespace std;

class CRectangle {
    int *width, *height;
  public:
    CRectangle (int,int);
    ~CRectangle ();
    int area () {return (*width * *height);}
};

CRectangle::CRectangle (int a, int b) {
  width = new int;
  height = new int;
  *width = a;
  *height = b;
}

CRectangle::~CRectangle () {
  delete width;
  delete height;
}

int main () {
  CRectangle rect (3,4), rectb (5,6);
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}



// overloading class constructors
#include <iostream>
using namespace std;

class CRectangle {
    int width, height;
  public:
    CRectangle ();
    CRectangle (int,int);
    int area (void) {return (width*height);}
};

CRectangle::CRectangle () {
  width = 5;
  height = 5;
}

CRectangle::CRectangle (int a, int b) {
  width = a;
  height = b;
}

int main () {
  CRectangle rect (3,4);
  CRectangle rectb; // do not include parentheses()
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  return 0;
}



// copy constructor
#include <iostream>
using namespace std;

class CRectangle {
    int width, height;
  public:
    CRectangle ();
    CRectangle (int,int);
    int area (void) {return (width*height);}
};

CRectangle::CRectangle () {
  width = 5;
  height = 5;
}

CRectangle::CRectangle (int a, int b) {
  width = a;
  height = b;
}

int main () {
  CRectangle rect (3,4);
  CRectangle rectb;
  CRectangle rectc(rectb); // copy constructor
  CRectangle rectd;
  rectd = rect; // copy assignment operator
  cout << "rect area: " << rect.area() << endl;
  cout << "rectb area: " << rectb.area() << endl;
  cout << "rectc area: " << rectc.area() << endl;
  cout << "rectd area: " << rectd.area() << endl;
  return 0;
}


// pointer to classes example
#include <iostream>
using namespace std;

class CRectangle {
    int width, height;
  public:
    void set_values (int, int);
    int area (void) {return (width * height);}
};

void CRectangle::set_values (int a, int b) {
  width = a;
  height = b;
}

int main () {
  CRectangle a, *b, *c;
  CRectangle * d = new CRectangle[2];
  b= new CRectangle;
  c= &a;
  a.set_values (1,2);
  b->set_values (3,4);
  d->set_values (5,6); // d or d[0].set..
  d[1].set_values (7,8);
  cout << "a area: " << a.area() << endl;
  cout << "*b area: " << b->area() << endl;
  cout << "*c area: " << c->area() << endl;
  cout << "d[0] area: " << d[0].area() << endl;
  cout << "d[1] area: " << d[1].area() << endl;
  delete[] d;
  delete b;
  return 0;
}




/******************************************************
2
Classes (II)
*/


// vectors: overloading operators example
#include <iostream>
using namespace std;

class CVector {
  public:
    int x,y;
    CVector () {};
    CVector (int,int);
    CVector operator + (CVector);
};

CVector::CVector (int a, int b) {
  x = a;
  y = b;
}

CVector CVector::operator+ (CVector param) {
  CVector temp;
  temp.x = x + param.x;
  temp.y = y + param.y;
  return (temp);
}

int main () {
  CVector a (3,1);
  CVector b (1,2);
  CVector c;
  c = a + b;
  cout << c.x << "," << c.y;
  return 0;
}



// overloading operators
#include <iostream>
using namespace std;

class CVector {
  public:
    int x,y;
    CVector () {x=0; y=0;};
    CVector (int,int);
    CVector operator - (CVector); // + -> - ,just a char
};

CVector::CVector (int a, int b) {
  x = a;
  y = b;
}

CVector CVector::operator - (CVector param) { // use operator - to add two...
  CVector temp;
  temp.x = x + param.x;
  temp.y = y + param.y;
  return (temp);
}

int main () {
  CVector a (3,1);
  CVector b (1,2);
  CVector c;
  c = a - b; // it is perfectly possible to do so.
  cout << c.x << "," << c.y;
  return 0;
}


// this
#include <iostream>
using namespace std;

class CDummy {
  public:
    int isitme (CDummy& param);
};

int CDummy::isitme (CDummy& param)
{
  if (&param == this) return true;
  else return false;
}

int main () {
  CDummy a;
  CDummy* b = &a;
  if ( b->isitme(a) )
    cout << "yes, &a is b";
  return 0;
}



// static members in classes
#include <iostream>
using namespace std;

class CDummy {
  public:
    static int n;
    CDummy () { n++; };
    ~CDummy () { n--; };
};

int CDummy::n=0;

int main () {
  CDummy a;
  CDummy b[5];
  CDummy * c = new CDummy;
  cout << a.n << endl;
  delete c;
  cout << CDummy::n << endl; //可以这样直接取
  cout << a.n << endl;
  return 0;
}



// global variable
#include <iostream>
using namespace std;
int n; // global variable

class CDummy {
  public:
    CDummy () { n++; };
    ~CDummy () { n--; };
};

int main () {
  n=0;
  CDummy a;
  CDummy b[5];
  CDummy * c = new CDummy;
  cout << n << endl;
  delete c;
  cout << n << endl;
  
  return 0;
}



/***********************************************************
3
Friendship and inheritance
*/


// friend functions
#include <iostream>
using namespace std;

class CRectangle {
    int width, height;
  public:
    void set_values (int, int);
    int area () {return (width * height);}
    friend CRectangle duplicate (CRectangle); //设外部函数为友
}; //这样这个外部函数就可以调用这个类中的私有成员了

void CRectangle::set_values (int a, int b) {
  width = a;
  height = b;
}

CRectangle duplicate (CRectangle rectparam) //这是外部函数
{
  CRectangle rectres;
  rectres.width = rectparam.width*2; // 可以直接调用 width
  rectres.height = rectparam.height*2; // 可以直接调用 height
  return (rectres);
}

int main () {
  CRectangle rect, rectb;
  rect.set_values (2,3);
  rectb = duplicate (rect);
  cout << rectb.area();
  return 0;
}



// friend class
#include <iostream>
using namespace std;

class CSquare; // an empty decaration of class CSquare

//长方形
class CRectangle {
    int width, height;
  public:
    int area ()
      {return (width * height);}
    void convert (CSquare a); //因为长方形是友，所以可以调用它
};
//正方形
class CSquare {
  private:
    int side;
  public:
    void set_side (int a)
      {side=a;}
    friend class CRectangle; //设长方形为友类
}; // 我要调用你，要你同意设我为友

void CRectangle::convert (CSquare a) {
  width = a.side; //如果非友，那么a.side是访问不到的
  height = a.side;
}
  
int main () {
  CSquare sqr;
  CRectangle rect;
  sqr.set_side(4); //已知正方形的边长
  rect.convert(sqr); //
  cout << rect.area(); //用长方形求面积的方法来求出
  return 0;
}



// derived classes 派生类
#include <iostream>
using namespace std;

class CPolygon { //多边形
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b;}
  };
  
//长方形
class CRectangle: public CPolygon { // public，起过滤作用。如为 private，则继承自 base class
  public:                           // 的各成员、函数，都将为 private ... 如不写，默认为 private
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon { //三角形
  public:
    int area ()
      { return (width * height / 2); }
  };
  
int main () {
  CRectangle rect;
  CTriangle trgl;
  rect.set_values (4,5); //子类可以调用父类的成员函数
  trgl.set_values (4,5);
  cout << rect.area() << endl;
  cout << trgl.area() << endl;
  return 0;
}



// constructors and derived classes
#include <iostream>
using namespace std;

class mother {
  public:
    mother ()
      { cout << "mother: no parameters
"; }
    mother (int a)
      { cout << "mother: int parameter
"; }
};

class daughter : public mother {
  public:
    daughter (int a)
      { cout << "daughter: int parameter

"; }
};

class son : public mother {
  public:
    son (int a) : mother (a) //先给父类参数。可以选择base class 的构造函数
      { cout << "son: int parameter

"; }
};

int main () {
  daughter cynthia (0); //先调用父类的默认构造函数，再调用自身
  son daniel(0); //先显式调用父类的带参数的构造函数，再调用自身
  
  return 0;
}


// multiple inheritance
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b;}
  };

class COutput {
  public:
    void output (int i);
  };

void COutput::output (int i) {
  cout << i << endl;
  }

class CRectangle: public CPolygon, public COutput { //继承自两个父类
  public:
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon, public COutput { //继承自两个父类
  public:
    int area ()
      { return (width * height / 2); }
  };
  
int main () {
  CRectangle rect;
  CTriangle trgl;
  rect.set_values (4,5); //调用一父
  trgl.set_values (4,5);
  rect.output (rect.area()); //调用二父
  trgl.output (trgl.area());
  return 0;
}



// multiple inheritance，三个
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b;}
  };

class COutput {
  public:
    void output (int i);
  };

void COutput::output (int i) {
  cout << i << endl;
  }
  
class COutputTest {
  public:
    void outputtest( int i ) {
      cout << "en,test again:) " << 2*i << endl;
    }
  };

class CRectangle: public CPolygon, public COutput { //继承自两个父类
  public:
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon, public COutput, public COutputTest { //继承自三个父类
  public:
    int area ()
      { return (width * height / 2); }
  };
  
int main () {
  CRectangle rect;
  CTriangle trgl;
  rect.set_values (4,5); //调用一父
  trgl.set_values (4,5);
  rect.output (rect.area()); //调用二父
  trgl.output (trgl.area());
  trgl.outputtest ( trgl.area() ); // 调用三父
  return 0;
}



/****************************************************
4
Polymorphism
*/


// pointers to base class
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
  };

class CRectangle: public CPolygon {
  public:
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area ()
      { return (width * height / 2); }
  };

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon * ppoly1 = &rect; //
  CPolygon * ppoly2 = &trgl; //
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  cout << rect.area() << endl;
  cout << trgl.area() << endl;
  return 0;
}



// virtual members
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area () //去掉virtual，输出全是0，因为调用子类的中的area失效。
      { return (0); }
  };

class CRectangle: public CPolygon {
  public:
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area ()
      { return (width * height / 2); }
  };

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon poly;
  CPolygon * ppoly1 = &rect;
  CPolygon * ppoly2 = &trgl;
  CPolygon * ppoly3 = &poly;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly3->set_values (4,5);
  cout << ppoly1->area() << endl;
  cout << ppoly2->area() << endl;
  cout << ppoly3->area() << endl;
  return 0;
}
//The member function area() has been declared as virtual in the base class because
// it is later redefined in each derived class. 


// virtual members -- 修改
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    int area () //去掉virtual，输出全是0，因为调用子类的中的area失效。
      { return (0); }
  };

class CRectangle: public CPolygon {
  public:
    int area ()
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area ()
      { return (width * height / 2); }
  };

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon poly;
  CRectangle * ppoly1 = &rect; //如果指针都对应上，那么就不用虚函数，不用多态继承了
  CTriangle * ppoly2 = &trgl;
  CPolygon * ppoly3 = &poly;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly3->set_values (4,5);
  cout << ppoly1->area() << endl;
  cout << ppoly2->area() << endl;
  cout << ppoly3->area() << endl;
  return 0;
}



// abstract base class
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area (void) =0; //抽象基类之虚函数
  };

class CRectangle: public CPolygon {
  public:
    int area (void)
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area (void)
      { return (width * height / 2); }
  };

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon * ppoly1 = &rect;
  CPolygon * ppoly2 = &trgl;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  cout << ppoly1->area() << endl;
  cout << ppoly2->area() << endl;
  return 0;
}



// pure virtual members can be called
// from the abstract base class
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area (void) =0; //抽象基类之纯虚成员
    void printarea (void)
      { cout << this->area() << endl; } // 根据指针的不同，调用不用的area()
  };

class CRectangle: public CPolygon {
  public:
    int area (void)
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area (void)
      { return (width * height / 2); }
  };

int main () {
  CRectangle rect;
  CTriangle trgl;
  CPolygon * ppoly1 = &rect;
  CPolygon * ppoly2 = &trgl;
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly1->printarea();
  ppoly2->printarea();
  return 0;
}


// dynamic allocation and polymorphism
#include <iostream>
using namespace std;

class CPolygon {
  protected:
    int width, height;
  public:
    void set_values (int a, int b)
      { width=a; height=b; }
    virtual int area (void) =0; //
    void printarea (void)
      { cout << this->area() << endl; }
  };

class CRectangle: public CPolygon {
  public:
    int area (void)
      { return (width * height); }
  };

class CTriangle: public CPolygon {
  public:
    int area (void)
      { return (width * height / 2); }
  };

int main () {
  CPolygon * ppoly1 = new CRectangle; //
  CPolygon * ppoly2 = new CTriangle;  //
  ppoly1->set_values (4,5);
  ppoly2->set_values (4,5);
  ppoly1->printarea();
  ppoly2->printarea();
  delete ppoly1;
  delete ppoly2;
  return 0;
}

  

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