line segments intersection

gistfile1.hpp

#include <cstdio>
#include <algorithm>
#include <cmath>

using namespace std;

struct point {
    double x,y;
    point ( double x = 0, double y = 0 ) : x(x),y(y) {}
    };

struct line {
    point p1,p2;

    void read (){
        scanf("%lf %lf %lf %lf",&p1.x,&p1.y,&p2.x,&p2.y);
        }

    };

double dx1,dy1,dx2,dy2;
double s,t;
point in;

void intersection ( line a, line b ){
    dx1 = a.p2.x - a.p1.x;
    dy1 = a.p2.y - a.p1.y;
    dx2 = b.p2.x - b.p1.x;
    dy2 = b.p2.y - b.p1.y;

    if ( fabs ( dx2 * dy1 - dx1 * dy2 ) < 0.0000001 ){
        printf("Paralelni\n");
        return;
        }
    s = (dx1 * (b.p1.y - a.p1.y) + dy1 * (a.p1.x - b.p1.x)) / double( dx2 * dy1 - dx1 * dy2 );
    t = (dx2 * (a.p1.y - b.p1.y) + dy2 * (b.p1.x - a.p1.x)) / double( dx1 * dy2 - dx2 * dy1 );

    if ( s<0 || s>1 || t<0 || t>1 )
        printf("Nemaju presjeka\n");
    else {
        in = point (a.p1.x + t * dx1, a.p1.y + t * dy1);
        printf("%lf %lf\n",in.x,in.y);
    }
    }

line a,b;

int main(){
    a.read();
    b.read();


    intersection ( a,b );


	return 0;
}