c++一些问题2.0 友元函数，运算符的重载

#include<iostream>
#include<string>
#include<cmath>
using namespace std;
class Triangle;
class Point {
 private:
     int x, y;
     friend  Triangle; //Triangle 是Point的友元类，Triangle 可以访问Point的所有成员
public:
    //友元函数声明，想要访问数据成员，必须传递对象的引用,通过对象访问类。
    friend double getLong(Point &x,Point &y); //不是成员函数，所以类外定义
    Point(int x, int y);
    void prit(Point &p1, Point &p2);
};

Point::Point(int x=0, int y=0) //构造函数
{
    this->x = x;
    this->y = y;
}

void Point::prit(Point &p1, Point &p2)
{
    cout  << sqrt((p1.x - p2.x)*(p1.x - p2.x) + (p1.y - p2.y)*(p1.y - p2.y)) << endl;
    
}
double getLong(Point &p1, Point &p2)
{
    double le;
    le = sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
    return le;
}


class Triangle
{
public:
    Triangle(Point &a, Point &b, Point &c);
                     //声明Point中的prit函数是Triangle的友元函数
    friend  void Point::prit(Point &p1, Point &p2);

    void getxy(int *p)
    {
        
        p[0] = c.x;
        p[1] = c.y;

    }

private:
     Point a, b, c; //Point类作为数据成员

};

Triangle::Triangle(Point &a, Point &b, Point &c) 
{
    this->a = a;
    this->b = b;
    this->c = c;
}

int main() 
{
    Point a(0, 0);
    Point b(3, 0);
    Point c(3, 4);

    Triangle t(a,b,c);
    cout << "三角形ab边长为:" ;
     a.prit(a, b);
     cout << "三角形ac边长为:" << getLong(a, c) << endl;
     int *p=new int[2];
     t.getxy(p);
     cout << "c的坐标为";
     cout<<"(" <<p[0] <<","<<p[1]<<")"<< endl;
    system("pause");
    return 0;
}

一般格式   函数类型 operator 运算符(形式参数){ code }

不能重载的有5个  .(成员访问运算符), *(成员指针访问运算符), ::(域运算符),
                 sizeof(长度运算符), ?:(条件运算符)

#include<iostream>
#include<string>
using namespace std;
class  Fraction {
private:
    int numerator; //分子
    int denominator; //分母
public:
    Fraction(int m, int n);
     void print();
    friend  Fraction operator + (Fraction &f1, Fraction &f2); //友元函数
    Fraction operator / (Fraction &f1);
};

// 构造函数
Fraction::Fraction(int m=0,int n=1) {
    numerator = m;
    denominator = n;
}

// 辗转相除法，求最大公约数。
int maxYueshu(int m, int n) {
    if (m < n) {  //保证m>n
        int temp = m;
        m = n;
       n = temp;
  }
    int r;
    while (true) {
        r = m %n;
        if (r == 0)
            break;
        m = n;
        n = r;
    }

    return n;
}

 //变成最简分数
void Fraction::print() {
    int gy= maxYueshu(numerator, denominator);

    cout << numerator/gy<<"/"<< denominator/gy << endl;
}
   //友元函数重载。
Fraction operator + (Fraction &f1, Fraction &f2) { //友元函数不属于类。
    Fraction f;
    f.numerator = f1.numerator*f2.denominator + f2.numerator*f1.denominator;
    f.denominator = f1.denominator*f2.denominator;
    return f;
}
               //成员函数重载
Fraction Fraction::operator / (Fraction &f1) {
    Fraction f;
    f.numerator = numerator*f1.denominator;
    f.denominator = denominator*f1.numerator;
    return f;
}

int main() {
    Fraction f1(8, 48);
    Fraction f2(6, 72);
    Fraction f3;
    cout << "f1+f2=";
    f3 = f1 + f2; //运算符+重载成功。
    f3.print();
    cout <<" f1 / f2=";
    f3 = f1 / f2;
    f3.print();
    system("pause");
    return 0;
}