poj 2007 极角排序

极角排序有四种方法，我一开始就是先算出极角来，然后进行排序，可交上去却是WA，现在还没有搞，后面用另一种还是错了，最后用了这种才过的！代码如下：#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>using namespace std;const int maxn=55;struct point{    double x,y;} p[maxn];double cross(point c1,point b1,point c2,point a2)//利用叉乘来判断是不是逆时针{    return (b1.x-c1.x)*(a2.y-c2.y)-(b1.y-c1.y)*(a2.x-c2.x);}bool cmp(point a,point b){    point c;    c.x=0;    c.y=0;    return cross(c,b,c,a)<0;}int main(){    int n=0;    while(scanf("%lf %lf",&p[n].x,&p[n].y)!=EOF)    {        ++n;    }    sort(p+1,p+n, cmp);    for(int i =0; i<n; i++)        cout<<"("<<p[i].x<<","<<p[i].y<<")"<<endl;    return 0;}