C++作业3

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项目二、友元函数

#include<iostream>  using namespace std;  #include<math.h>  class Distance{     private:          double x;        double y;      public:         Distance(double xx=0,double yy=0):x(xx),y(yy){}      double distance1();      friend double distance2(Distance &);      double get_x();      double get_y();  };   double Distance::distance1()  {      double distance;      distance=sqrt(x*x+y*y);      return distance;  }  double distance2(Distance &c)  {      double distance;      distance=sqrt(c.x*c.x+c.y*c.y);      return distance;  }  double Distance::get_x()  {      return x;  }  double Distance::get_y()  {      return y;  }  double distance3(Distance &c)  {      double distance,a,b;      a=c.get_x();      b=c.get_y();      distance=sqrt(a*a+b*b);      return distance;  }  int main()  {     Distance c1(3.0,4.0);      cout<<"distance is :"<<c1.distance1()<<endl;      cout<<"distance is :"<<distance2(c1)<<endl;      cout<<"distance is :"<<distance3(c1)<<endl;      return 0;  }

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