#include
class POINT
{
public;
Point(double a,double b){ x=a;y=b};
fiend double square(Point &a,Point &b);
private:
double x,y;
};
double square(Point &a,Point &b) { return sqr((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y))};
void main()
{
Point p1(x1,y1),p2(x2,y2);
double l;
l=square(p1,p2);
}