类与对象

类相当于一个模板，而对象就是依据类这个模板打造出来的可以使用的工具。类是对象的抽象，对象是类的具体化。

构造函数与析构函数

• 构造函数用来初始化一个对象，构造和默认构造两种。

• 构造函数与析构函数的调用对等

  矩形

  #include<iostream>
  using namespace std;
  class Rectangle{
  double length,width;
  public :
      Rectangle();
      Rectangle(double l,double w);
      Rectangle(const Rectangle &);
      ~Rectangle();
      double getArea();
      void setData(double ,double);
  };
  Rectangle::Rectangle(double l,double w):length(l),width(w){
  cout<<"构造一个Rectangle对象"<<endl;
  }
  Rectangle::Rectangle():Rectangle(1.0,2.0){
  }
  Rectangle::Rectangle(const Rectangle &r)
  {
  length=r.length;
  width=r.width;
  cout<<"复制构造一个Rectangle对象"<<endl; 
  } 
  Rectangle::~Rectangle()
  {
  cout<<"析构一个Rectangle对象"<<endl;
  }
  double Rectangle::getArea()
  {
  return length*width;
  }
  void Rectangle::setData(double l,double w)
  {
  length=l;
  width=w;
  }
  int main()
  {
  Rectangle r1;
  Rectangle r2(5.0,6.0);
  cout<<"r1的面积是："<<r1.getArea()<<endl;
  cout<<"r2的面积是："<<r2.getArea()<<endl;
  cout<<"重新设置r1的长和宽。"<<endl;
  double l,w;
  cin>>l>>w;
  r1.setData(l,w);
  cout<<"修改后r1的面积为："<<r1.getArea()<<endl;
  return 0;
   }  

  

  Complex

  #include<iostream>
  using namespace std;
  class Complex{
  double real,imaginary;
  public :
      Complex(double r,double i);
      Complex(double r);
      Complex();
      Complex(const Complex &c);
      ~Complex();
      void set(double r,double i);
      void add(const Complex &c);
      void show();
  };
  Complex::Complex(double r,double i):real(r),imaginary(i){
  cout<<"构造一个Complex对象"<<endl; 
  }
  Complex::Complex(double r):real(r),imaginary(0){
  cout<<"构造一个Complex对象"<<endl;
  }
  Complex::Complex():Complex(0,0){
  }
  Complex::Complex(const Complex &c)
  {
  real=c.real;
  imaginary=c.imaginary;
  cout<<"复制构造一个Complex对象"<<endl;
  }
  Complex::~Complex()
  {
  cout<<"析构一个Complex对象"<<endl;
  }
  void Complex::set(double r,double i)
  {
  real=r;
  imaginary=i;
  }
  void Complex::add(const Complex &c)
  {
  real+=c.real;
  imaginary+=c.imaginary;
  }
  void Complex::show()
  {
  cout<<real<<"+"<<imaginary<<"i"<<endl;
  }
  int main()
  {
  Complex c1(3.5,4.5);
  Complex c2;
  Complex c3=3;
  cout<<"c1: ";
  c1.show();
  cout<<"c2: ";
  c2.show();
  cout<<"c3: ";
  c3.show();
  c2.set(5.6,3.5);
  cout<<"new c2: ";
  c2.show();
  c1.add(c3);
  cout<<"c1+c3=";
  c1.show();
  c3.add(c2);
  cout<<"c3+c2=";
  c3.show();
  return 0;
   }