C语言平面几何5-两点确定一条直线

/* 两个不同点A,B确定一条直线，AB相同返回的值全0
*  直线方程：Ax+By+c=0
*  A = y2 - y1;
*  B = x1 - x2;
*  C = -A*x1 - B*y1 = x2*y1 - x1*y2;
*/
Line LineMake(Point A, Point B)
{
Line l;
l.A = B.y - A.y;
l.B = A.x - B.x;
l.C = B.x * A.y - A.x * B.y;
return l;
}