判断线段规范相交

算是学了一个模版吧

#include<stdio.h>

#include<string.h>

#include<stdlib.h>

#include<math.h>



const double eps = 1e-8;

struct point

{

    double x, y;

};



point a, b, c, d;



inline int dcmp(double d)

{

    if(fabs(d) < eps) return 0;

    return d > 0 ? 1 : -1;

}



inline double det(double x1, double y1, double x2, double y2)

{

    return x1 * y2 - x2 * y1;

}



inline double cross(point a, point b, point c)

{

    return det(b.x - a.x, b.y - a.y, c.x - a.x, c.y - a.y);

}



inline int segcross(point a, point b, point c, point d)

{

    return ((dcmp(cross(a, c, d)) ^ dcmp(cross(b, c, d))) == -2

        &&  (dcmp(cross(c, a, b)) ^ dcmp(cross(d, a, b))) == -2);



}



int main()

{

    while(scanf("%lf%lf%lf%lf", &a.x, &a.y, &b.x, &b.y) != EOF)

    {

        scanf("%lf%lf%lf%lf", &c.x, &c.y, &d.x, &d.y);

        if(segcross(a, b, c, d))

            printf("Yes\n");

        else

            printf("No\n");

    }

    return 0;

}