infoarena

const fis='geometry';
      nmax=500;
var x1,x2,y1,y2,a,b,c:array[1..nmax] of longint;
    n,rez:longint;

Procedure read_data;
var i:longint;
begin
readln(n);
for i:=1 to n do
    begin
    readln(x1[i],y1[i],x2[i],y2[i]);
    a[i]:=y2[i]-y1[i];
    b[i]:=x2[i]-x1[i];
    c[i]:=(x1[i]*y2[i])-(x2[i]*y1[i]);
    end;
end;

Procedure compute;
var i,j:longint;
    y:real;

Function peg(n1,n2:longint):boolean;
begin
if a[n1]*b[n2]=a[n2]*b[n1]
then peg:=true
else peg:=false;
end;

Function ini(aa,bb:longint;c:real):boolean;
var a,b:longint;
begin
if aa<=bb
then begin
     a:=aa;
     b:=bb;
     end
else begin
     a:=bb;
     b:=aa;
     end;
if (a<=c) and (c<=b)
then ini:=true
else ini:=false;
end;

begin
for i:=2 to n do
    for j:=1 to i-1 do
        if peg(i,j)
        then begin
             if (c[i]=c[j]) and (ini(x1[i],x2[i],x1[j]) or
             ini(x1[i],x2[i],x2[j]) or ini(x1[j],x2[j],x1[i]) or ini(x1[j],x2[j],x2[i]))
             then inc(rez);
             end
        else begin
             y:=((c[j]*a[i])-(c[i]*a[j]))/((b[i]*a[j])-(b[j]*a[i]));
             if ini(y1[i],y2[i],y) and ini(y1[j],y2[j],y)
             then inc(rez);
             end;
end;

begin
assign(input,fis+'.in');
reset(input);
assign(output,fis+'.out');
rewrite(output);
read_data;
compute;
writeln(rez);
close(output);
close(input);
end.

#include<cstdio>
using namespace std;
int n,nr,i,j,a[3],b[3],c[3],x1[502],x2[502],y1[502],y2[502];
double m[503];
double av,bv,eps;
double abs(double val)
{
	if(val<0) return val*-1;
	return val;
}
void detec(int x1,int y1,int x2,int y2,int p)
{
	a[p]=y1-y2;
	b[p]=x2-x1;
	c[p]=x1*y2-y1*x2;
}
void inter(int a1,int b1,int a2,int b2,int x1,int y1,int x2,int y2)
{
	detec(a1,b1,a2,b2,1);
	detec(x1,y1,x2,y2,2);
	bv=double(c[2]*a[1]-c[1]*a[2])/(b[1]*a[2]-b[2]*a[1]);
	av=double(-b[1]*bv-c[1])/a[1];
}
int ap(int x1,int y1,int x2,int y2,double a2,double b2)
{
	if((a2>=x1&&a2<=x2)||(a2<=x1&&a2>=x2)) ;
	else return 0;
	if((b2>=y1&&b2<=y2)||(b2<=y1&&b2>=y2)) ;
	else return 0;
	return 1;
}
int main()
{
freopen("geometry.in","r",stdin);
freopen("geometry.out","w",stdout);
scanf("%d",&n);
eps=0.0001;
for(i=1;i<=n;i++)
{
	scanf("%d",&x1[i]);
	scanf("%d",&y1[i]);
	scanf("%d",&x2[i]);
	scanf("%d",&y2[i]);
	if(x2[i]!=x1[i]) m[i]=(double)(y2[i]-y1[i])/(x2[i]-x1[i]);
	else m[i]=-1;
}
for(i=1;i<=n;i++)
	for(j=i+1;j<=n;j++)
	{
		if((double)abs((double)m[i]-m[j])>eps)
		{
			inter(x1[i],y1[i],x2[i],y2[i],x1[j],y1[j],x2[j],y2[j]);
			if(ap(x1[i],y1[i],x2[i],y2[i],av,bv)==1&&ap(x1[j],y1[j],x2[j],y2[j],av,bv)==1) nr++;
		}
		else
		//{
			//detec(x1[i],y1[i],x2[i],y2[i],1);
			if(ap(x1[i],y1[i],x2[i],y2[i],x1[j],y1[j])==1||ap(x1[i],y1[i],x2[i],y2[i],x2[j],y2[j])==1) nr++;
		//}
	}
printf("%d\n",nr);
return 0;
}

#include<algorithm>
#include<fstream>
using namespace std;
ifstream f("geometry.in");
ofstream g("geometry.out");
int i,e,j,n,nr,ok,v[200];
struct pc{int x,y;};
pc a[510],b[510];
int s(pc a,pc b,pc c)
{
    return a.y*(c.x-b.x)-a.x*(c.y-b.y)+b.x*c.y-c.x*b.y;
}
int inter(pc a1,pc b1,pc a2,pc b2)
{
    return (s(a2,a1,b1)*s(b2,a1,b1)<=0&&s(a1,a2,b2)*s(b1,a2,b2)<=0);
}
int main()
{
    f>>n;
    for(i=1;i<=n;++i)
    {
        f>>a[i].x>>a[i].y>>b[i].x>>b[i].y;
    }
    for(i=1;i<=n;++i)
    for(j=i+1;j<=n;++j)
    if(inter(a[i],b[i],a[j],b[j]))
    ++nr;
    g<<nr<<'\n';
    return 0;
}

#include<algorithm>
#include<fstream>
using namespace std;
ifstream f("geometry.in");
ofstream g("geometry.out");
int i,e,j,n,nr,ok,v[200];
struct pc{double x,y;};
pc a[510],b[510];
double s(pc a,pc b,pc c)
{
    return a.y*(c.x-b.x)-a.x*(c.y-b.y)+b.x*c.y-c.x*b.y;
}
double inter(pc a1,pc b1,pc a2,pc b2)
{
    return (s(a2,a1,b1)*s(b2,a1,b1)<=0&&s(a1,a2,b2)*s(b1,a2,b2)<=0);
}
int main()
{
    f>>n;
    for(i=1;i<=n;++i)
    {
        f>>a[i].x>>a[i].y>>b[i].x>>b[i].y;
    }
    for(i=1;i<=n;++i)
    for(j=i+1;j<=n;++j)
    if(inter(a[i],b[i],a[j],b[j]))
    ++nr    g<<nr<<'\n';
    return 0;
}

3
0 -2 0 2
0 0 2 0
0 3 2 0