圆在平面上是怎样定义的

圆在平面上是怎样定义的

#include typedef struct PP {double x,y;}POINT; typedef struct CC {POINT O; double r;}CIRCLE; int incircle(POINT p,CIRCLE c1) {return ((p.x-c1.O.x)*(p.x-c1.O.x)+(p.y-c1.O.y)*(p.y-c1.O.y)<=c1.r*c1.r);} int main() {POINT p1,p2; CIRCLE C; p1.x=1.0; p1.y=1.0; p2.x=-1.0; p2.y=2.0; C.O.x=0; C.O.y=0; C.r=2.0; printf("%d\n",incircle(p1,C)); printf("%d\n",incircle(p2,C)); return 0; }