极角排序，其实是叉乘排序

 

#include 
    
     #include 
     
      #include 
      
       #include 
       
        using namespace std;#define eps 1e-8struct point{	double x, y;} s;double getangle(point a){	return atan2(a.y, a.x);}double xmult(point p1, point p2, point p0){	return (p1.x - p0.x)*(p2.y - p0.y) - (p2.x - p0.x)*(p1.y - p0.y);}bool operator < (point a, point b){	return xmult(a, b, s) > eps;}int main(){	vector
        
          p;	double a, b;	//freopen("D:\\b.txt", "r", stdin);	cin >> s.x >> s.y;	while (cin >> a >> b)	{		point temp;		temp.x = a, temp.y = b;		p.push_back(temp);	}	sort(p.begin(), p.end());	cout << "(0,0)" << endl;	for (vector
         
          ::iterator it = p.begin(); it != p.end(); ++it) { cout << '(' << (*it).x << ',' << (*it).y << ')' << endl; }}