今天偶然写两个灰常简单的类，Point，Rectangle，即左上角和右下角标识一个矩形的类。

#include <iostream>

class Point{

public:

Point();

Point(int x);

Point(int x,int y);

int getX();

int getY();

void setX(int new_val);

void setY(int new_val);

void printPoint();

private:

int x;

int y;

};

Point::Point(int x):x(x),y(x){};

Point::Point():x(0),y(0){};

Point::Point(int x,int y):x(x),y(y)

{

};

int Point::getX(){

return x;

}

int Point::getY(){

return y;

}

void Point::setX(int new_val){

x = new_val;

}

void Point::setY(int new_val){

y = new_val;

}

void Point::printPoint(){

std::cout<<"X:"<<x<<",Y:"<<y<<std::endl;

}

int abss(int x,int y){

if(x-y>0){

return x-y;

}else{

return y-x;

}

}

class Rectangle{

public:

Rectangle(Point &lf,Point &rd);

int Calmian();

int Calzhou();

Point &getlu();

private:

Point leftup;

Point rightdown;

};

Point &Rectangle::getlu(){

return leftup;

}

Rectangle::Rectangle(Point &lf,Point &rd):leftup(lf),rightdown(rd){};

int Rectangle::Calmian(){

int x1,x2,y1,y2;

x1 = leftup.getX();

y1 = leftup.getY();

x2 = rightdown.getX();

y2 = rightdown.getY();

return (abss(x1,x2))*(abss(y1,y2));

}

int Rectangle::Calzhou(){

int x1,x2,y1,y2;

x1 = leftup.getX();

y1 = leftup.getY();

x2 = rightdown.getX();

y2 = rightdown.getY();

return 2*(abss(x1,x2)+abss(y1,y2));

}

 

 

 

标红部分一开始没有使用引用，导致test.getlu().setX(9);  该点并未有任何改变，即以by-value的传递方式，getlu()的只是矩形左上点的一个““副本””，并没有真正改变它。

  这个概念上一直记得，写的时候却不记得了，Mark下下。。。