POJ2007+几何+极角排序

/*
几何+凸包逆序输出+极角排序
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<algorithm>
using namespace std;
const int maxn = 55;
const double eps = 1e-8;
struct Point{
    double x,y;
};
Point point[ maxn ];

double xmult( Point sp,Point ep,Point op ){
    return ( sp.x-op.x )*( ep.y-op.y )-( sp.y-op.y )*( ep.x-op.x );
}

int sig( double d ){
    if( d>eps ) return 1;
    if( d<-eps ) return -1;
    return 0;
}

double dist( Point a,Point b ){
    double sum = ( a.x-b.x )*( a.x-b.x )+( a.y-b.y )*( a.y-b.y );
    return sqrt( sum );
}

int cmp(  Point a, Point b ){
    return sig( xmult(a,b,point[0]) )>0;
}

int main(){
    int n = 0;
    while( scanf("%lf%lf",&point[ n ].x,&point[ n ].y )!=EOF )
        n++;
    sort( point+1,point+n,cmp );
    for( int i=0;i<n;i++ ){
        printf("(%.0lf,%.0lf)\n",point[ i ].x,point[ i ].y);
    }
    return 0;
}