UVA 10242 Fourth Point !!

Title description

This question is relatively simple, given the coordinates of three points of the parallelogram, find the coordinates of the fourth point

#include<iostream>
using namespace std;
typedef struct{
    
    
	double x,y;
}point;
int main(){
    
    
	point a,b,c,d,e;
	while(~scanf("%lf%lf%lf%lf",&a.x,&a.y,&b.x,&b.y))
     {
    
    
     	~scanf("%lf%lf%lf%lf",&c.x,&c.y,&d.x,&d.y);
     	if(a.x==c.x&&a.y==c.y)
     	swap(a,b);
     	if(a.x==d.x&&a.y==d.y)
     	{
    
    
     		swap(a,b);
		    swap(c,d);
		}
		if(b.x==d.x&&b.y==d.y)
		swap(c,d);
		e.x=a.x+d.x-c.x;
		e.y=a.y+d.y-c.y;
		printf("%.3lf %.3lf\n",e.x,e.y);
     	
	 }
	 return 0;
}