Go: package main

import "fmt"

func main() {
	var x1, x2, x3, y1, y2, y3, xp, yp float64
	for {
		v, _ := fmt.Scanf("%f %f %f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3, &xp, &yp)
		// println(x1, x2, x3, y1, y2, y3, xp, yp)
		if v != 8 {
			break
		}
		ok1 := true
		ok2 := true
		if (x2-x1)*(yp-y1)-(xp-x1)*(y2-y1)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if (x3-x2)*(yp-y2)-(xp-x2)*(y3-y2)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if (x1-x3)*(yp-y3)-(xp-x3)*(y1-y3)<0 {
			ok1 = false
		} else {
			ok2 = false
		}
		if ok1 || ok2 {
			fmt.Println("YES")
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include <bits/stdc++.h>
using namespace std ;

#define pb(n) push_back(n)
#define fi first
#define se second
#define X real()
#define Y imag()
#define all(r) (r).begin(),(r).end()
#define gsort(st,en) sort((st),(en),greater<int>())
#define vmax(ary) *max_element(all(ary))
#define vmin(ary) *min_element(all(ary))
#define debug(x) cout<<#x<<": "<<x<<endl
#define fcout(n) cout<<fixed<<setprecision((n))
#define scout(n) cout<<setw(n)
#define vary(type,name,size,init) vector< type> name(size,init)

#define rep(i,n) for(int i = 0; i < (int)(n);++i)
#define REP(i,a,b) for(int i = (a);i < (int)(b);++i)
#define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it)
#define repa(n,array) for(auto &n :(array))

using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using dict = map<string,int>;
using comd = complex<double>;
using pii = pair<int,int> ;

constexpr int imax = ((1<<30)-1)*2+1 ;
constexpr int inf = 100000000;
constexpr double PI = acos(-1.0) ;
double eps = 1e-10 ;
const int dy[] = {-1,0,1,0};
const int dx[] = {0,-1,0,1};

inline bool value(int x,int y,int w,int h){
  return (x >= 0 && x < w && y >= 0 && y < h);
}

double CalcDist(comd p1, comd p2){
  return sqrt(pow(p1.X - p2.X,2.0) + pow(p1.Y -p2.Y,2.0));
}

template<typename T>
void Unique(vector<T> &v){
  sort(all(v));
  v.erase(all(v),v.end());
}

template<typename T>
T ston(string& str, T n){
  istringstream sin(str) ;
  T num ;
  sin >> num ;
  return num ;
}

void Ans(bool f){
  if(f) cout << "YES"<<endl;
  else cout << "NO"<<endl;
}

double EPS = 1e-10;
double add(double a, double b){
  if(abs(a+b) < EPS* (abs(a) + abs(b))) return 0;
  return a+b;
}
struct P{
  double x,y;
  P(){}
  P(double _x,double _y):x(_x),y(_y){}
  P operator + (P p){
    return P(add(x,p.x) ,add(y,p.y));
  }
  P operator - (P p){
    return P(add(x,-p.x) ,add(y,-p.y));
  }
  P operator * (double d){
    return P(x * d,y * d);
  }
  double dot(P p){
    return add(x * p.x,y*p.y);
  }
  double det(P p){
    return add(x*p.y,-y*p.x);
  }
  double dist2(P p){
    return ((*this-p).x * (*this-p).x) + ((*this-p).y * (*this-p).y);
  }
  double GetSlope(P &p){
    P tmp = *this - p;
    return tmp.y/tmp.x;
  }
};
//???????????????????????¨?????????
bool on_seg(P p1,P p2,P q){
  return (p1-q).det(p2-q) == 0 && (p1-q).dot(p2-q) <= 0;
}
int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  double a,b,c,d,e,f,xp,yp;
  while(cin >> a >> b >> c >> d >> e >> f >> xp >> yp){
    bool flag = true;
    double acx = c-a,abx = e-a,acy = d-b,aby = f-b,apx = xp-a,apy = yp - b;
    P p1 = P(a,b),p2 = P(c,d),p3 = P(e,f),p4 = P(xp,yp);
    double t,s;
    if(acx == 0){
      s = apx/ abx;
      t = (apy - s * aby)/acy;
    }
    else if(acy == 0){
      s = apy/aby;
      t = (apx - s * abx)/acx;
    }
    else if(abx == 0){
      t = apx / acx;
      s = (apy- t * acy)/aby;
    }
    else if(aby == 0){
      t = apy/acy;
      s = (apx - t * acx)/abx;
    }
    else{
      t = (abx * apy - apx * aby)/(acy - acx*aby);
      s = (apx - t * acx)/abx;
    }
    debug(s);
    debug(t);
    if(on_seg(p1,p2,p4) || on_seg(p1,p3,p4) || on_seg(p2,p3,p4)){
      flag = false;
    }
    else{
      flag = 0 < t+s && t+s < 1 && s > 0 && t > 0;
    }
    Ans(flag);
  }
  return 0;
}

C++: #include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
#include <cmath>
#include <complex>
#include <map>
using namespace std;
 
#define rep(i,n) for(int i=0;i<int(n);++i)
 
static const double PI=6*asin(0.5);
typedef complex<double> P;
typedef long long ll;
static const double eps = 1e-8;
 
double x[3],y[3];
double xp,yp;
 
double dist(P a,P b){
    return (sqrt((real(a)-real(b))*(real(a)-real(b))+(imag(a)-imag(b))*(imag(a)-imag(b))));
}
 
double tri_pro(P a,P b,P c){
    double aa,bb,cc;
    aa = dist(b,c);
    bb = dist(c,a);
    cc = dist(a,b);
    double s = (aa+bb+cc)/2.0;
    return sqrt(s*(s-aa)*(s-bb)*(s-cc));
}
 
 
int main(){
    //P a(0.0,0.0),b(4.0,0.0),c(4.0,2.0);
    //cout<<tri_pro(a,b,c)<<endl;
    
    
    
    while(cin>>x[0]>>y[0]){
        rep(i,2) cin>>x[i+1]>>y[i+1];
        cin>>xp>>yp;
        P a(x[0],y[0]),b(x[1],y[1]),c(x[2],y[2]);
        P p(xp,yp);
        double sa,sb,sc;
        sa = tri_pro(b,c,p);
        sb = tri_pro(c,a,p);
        sc = tri_pro(a,b,p);
        double s = tri_pro(a,b,c);
        //cout<<"s="<<s<<"\nsa sb sc "<<sa<<" "<<sb<<" "<<sc<<endl;
        if((int)(s)-(int)(sa+sb+sc)==0) cout<<"YES\n";
        else cout<<"NO\n";
    }
    
    return 0;
}

C++: #include<cmath>
#include<algorithm>
#include<iostream>
#include<vector>
#include<climits>
#include<cfloat>

using namespace std;

double EPS = 1e-10;

double add(double a, double b){
  if(abs(a+b) < EPS * (abs(a)+abs(b)))return 0;
  return a+b;
}

struct point{
  double x, y;
  point(){}
  point(double x,double y) : x(x) , y(y){}

  point operator + (point p){
    return point(add(x,p.x), add(y,p.y));
  }

  point operator - (point p){
    return point(add(x,-p.x), add(y,-p.y));
  }

  point operator * (double d){
    return point(x*d,y*d);
  }
};

double dot(point a, point b) {
  return (a.x * b.x + a.y * b.y);
}

double cross(point a, point b) {
  return (a.x * b.y - a.y * b.x);
}

int is_point_on_line(point a, point b, point c) {
  return cross(b-a, c-a)==0.0 &&
         (dot(b-a, c-a) > -EPS) &&
         (dot(a-b, c-b) > -EPS);
}

int is_intersected_ls(point a1, point a2, point b1, point b2) {

  if(cross(a1-a2,b1-b2)==0){
    return is_point_on_line(a1,a2,b1) || is_point_on_line(a1,a2,b2) 
        || is_point_on_line(b1,b2,a1) || is_point_on_line(b1,b2,a2);
  }
  else {
    return ( cross(a2-a1, b1-a1) * cross(a2-a1, b2-a1) < EPS ) &&
           ( cross(b2-b1, a1-b1) * cross(b2-b1, a2-b1) < EPS );
  }
}

int inside(point p, vector<point> ps){
  point a,b;
  a=b=p;

  b.x=1000000;

  int n=ps.size();
  ps.push_back(ps[0]);

  double ymx=-DBL_MAX,ymn=DBL_MAX;
  for(int i=0;i<n;i++){
    ymx=max(ymx,ps[i].y);
    ymn=min(ymn,ps[i].y);
  }
  if(a.y<=ymn||a.y>=ymx)return 0;
  
  for(int i=0;i<n;i++){
    if(is_point_on_line(ps[i],ps[i+1],p))return 0;
  }
  
  int cnt1=0;
  for(int i=0;i<n;i++)
    if(is_point_on_line(a,b,ps[i]))cnt1++;
  
  int cnt=0;
  for(int i=0;i<n;i++)
    if(is_intersected_ls(ps[i],ps[i+1],a,b))cnt++;
  
  return (cnt-cnt1)%2;
}

int main(void){
 
  point in[4],p;
  vector<point>ps;

  while(cin>>in[1].x>>in[1].y>>in[2].x>>in[2].y>>in[3].x>>in[3].y>>p.x>>p.y){

    ps.clear();

    for(int i=1;i<4;i++)
    ps.push_back(in[i]);

    if(inside(p,ps))cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <complex>
#include <cmath>
using namespace std;
typedef complex<double> xy_t;
double cross_product(xy_t a, xy_t b){ return (conj(a)*b).imag();}
double x[4],y[4];
int main() {
	while(true){
		for(int i=0; i<4;++i) cin >> x[i] >> y[i];
		if(!cin) break;
		xy_t a(x[0],y[0]),b(x[1],y[1]),c(x[2],y[2]),p(x[3],y[3]);
		bool ok = cross_product(a-p,b-p)*cross_product(b-p,c-p)>0
				  && cross_product(b-p,c-p)*cross_product(c-p,a-p)>0;
		cout << (ok ? "YES" : "NO") << endl;
	}
	return 0;
}