"Convex-clad Graham-method pole-angle Sort" POJ-scrambled Polygon

link:http://poj.org/problem?id=2007

Graham method for Convex Hull (O (nlog2n))

/* Extreme Corner Sort */
#include <cstdio>
#include <cmath>
#include <algorithm>
using namespace STD;

const int N = +;
Const double EPS = 1e-6;
struct point
{
    double x, y;
};
Point A[n];
Whether to turn left Strictly, collinear does not count (fork multiply)
double xmult (point a,point b,point C)   //(CA) x (CB)
{
    return (a.x-c.x) * (b.y-c.y )-(b.x-c.x) * (A.Y-C.Y);
}
Sort sort Function
bool CMP (const point &a, const point &b)//Counter-clockwise sort
{Point
    origin;
    Set the origin point
    origin.x = ORIGIN.Y = 0;
    Return Xmult (origin,b,a) <eps;
}

int main ()
{
    int n=0;
    while (scanf ("%lf%lf", &a[n].x,&a[n].y)!=eof)
        ++n;
    A polar sort, the first empty past
    sort (a+1,a+n,cmp);
    for (int i=0; i<n; ++i)
        printf ("(%.0LF,%.0LF) \ n", a[i].x,a[i].y);
    return 0;
}