hdoj1086 You can Solve a Geometry Problem too

#include<iostream>
#include<stdio.h>
using namespace std;
int n;
typedef struct {        //定义点
    double x, y;
} point;
struct segment {
    point fir, end;
};
segment pnt[100];
bool inter(point & a, point & b, point & c, point & d)
{
    if (min(a.x, b.x) > max(c.x, d.x) || min(a.y, b.y) > max(c.y, d.y) ||
    min(c.x, d.x) > max(a.x, b.x) || min(c.y, d.y) > max(a.y, b.y))
    return 0;
    double h, i, j, k;
    h = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
    i = (b.x - a.x) * (d.y - a.y) - (b.y - a.y) * (d.x - a.x);
    j = (d.x - c.x) * (a.y - c.y) - (d.y - c.y) * (a.x - c.x);
    k = (d.x - c.x) * (b.y - c.y) - (d.y - c.y) * (b.x - c.x);
    return h * i <= 0.0000000001 && j * k <= 0.0000000001;
}

int main()
{
    while (scanf("%d", &n) != EOF && n) {
    int sum = 0;
    for (int i = 0; i < n; ++i) {
        scanf("%lf%lf%lf%lf", &pnt[i].fir.x, &pnt[i].fir.y,
          &pnt[i].end.x, &pnt[i].end.y);
    }
    for (int i = 0; i < n; ++i) {
        for (int j = i + 1; j < n; ++j) {
        if (inter(pnt[i].fir, pnt[i].end, pnt[j].fir, pnt[j].end))
            sum++;
        }
    }
    printf("%d\n", sum);
    }
}