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 <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <algorithm>

using namespace std;

#define rep(i,j) REP((i), 0, (j))
#define REP(i,j,k) for(int i=(j);(i)<(k);++i)
#define BW(a,x,b) ((a)<=(x)&&(x)<=(b))
#define MP make_pair
#define PB push_back
#define F first
#define S second
#define INF 1 << 30
#define EPS 1e-10

typedef pair<int, int> pi;
typedef pair<int, pi> pii;
typedef vector<int> vi;
typedef queue<int> qi;
typedef long long ll;

struct point{ double x, y; };

int ccw(point p0, point p1, point p2){
  double dx1, dx2, dy1, dy2;
  dx1 = p1.x - p0.x; dy1 = p1.y - p0.y;
  dx2 = p2.x - p0.x; dy2 = p2.y - p0.y;
  if(dx1*dy2 > dy1*dx2) return 1;
  if(dx1*dy2 < dy1*dx2) return -1;
  if((dx1*dx2 < 0) || (dy1*dy2 < 0)) return -1;
  if((dx1*dx1+dy1*dy1) < (dx2*dx2+dy2*dy2)) return 1;
  return 0;
}

int main(){
  double x1, x2, x3, xp, y1, y2, y3, yp;
  while(~scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3, &xp, &yp) && x1+y1+x2+y2+x3+y3+xp+yp){
    point a, b, c, P;
    a.x = x1; a.y = x1;
    b.x = x2; b.y = y2;
    c.x = x3; c.y = y3;
    P.x = xp; P.y = yp;
    if(ccw(a, b, P) == ccw(b, c, P) && ccw(b, c, P) == ccw(c, a, P)) puts("YES");
    else puts("NO");
  }
  return 0;
}

C++: #include<cstdio>
#include<cmath>
using namespace std;

int main(){
	double a,b,c,d,e,f,p,q;
	bool j;
	while( scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&a,&b,&c,&d,&e,&f,&p,&q) != EOF ){
		if( (q==(b-d)/(a-c)*p-(a*d-b*c)/(c-a))||
			(q==(d-f)/(c-e)*p-(c*f-d*e)/(e-c))||
			(q==(f-b)/(e-a)*p-(e*b-a*f)/(a-e))){
				printf("NO\n");
		}
		else{
			j = true;
			if(a==c){
				if(!(p>a==e>a))j=false;
			}
			else{
				if( !( (q>(b-d)/(a-c)*p-(a*d-b*c)/(c-a))==(f>=(b-d)/(a-c)*e-(a*d-b*c)/(c-a)) ) )j=false;
			}
			if(c==e){
				if(!(p>c==a>c))j=false;
			}
			else{
				if(!( (q>(d-f)/(c-e)*p-(c*f-d*e)/(e-c))==(b>=(d-f)/(c-e)*a-(c*f-d*e)/(e-c)) ))j=false;
			}
			if(e==a){
				if(!(p>e==c>e))j=false;
			}
			else{
				if(!( (q>(f-b)/(e-a)*p-(e*b-a*e)/(a-e))==(d>=(f-b)/(e-a)*c-(e*b-a*f)/(a-e)) ))j=false;
			}
			if(j){
				printf("YES\n");
			}
			else{
				printf("NO\n");
			}
		}
	}
	return 0;
}

C++: //二次元幾何ライブラリ
#include <iostream>
#include <complex>
#include <map>
#include <vector>

using namespace std;

#define rep(i, n) for (int i = 0; i < int(n); ++i)
#define x(a) (a).real()
#define y(a) (a).imag()
typedef long double D;
typedef bool B;
typedef complex<D> P;   //点
typedef complex<D> V;   //ベクトル
typedef pair<P,P>  L;   //直線
typedef pair<P,D>  C;   //円
typedef vector<P>  Pol; //多角形

//変数名定義
const D INF = 1e100;
const D EPS = 1e-8;
const D PI = acos(-1);

template<class T> bool operator==(T a, T b){return abs(a - b )< EPS;}
template<class T> int sig(T r) {return (r==0||r==-0) ? 0 : r > 0 ? 1 : -1;}

  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }

// ベクトルaの絶対値を求める
// D Length = abs(a);

// 2点a,b間の距離を求める
// D Distance = abs(a-b); 

// 内積 (Inner Product) : a・b = |a||b|cosθ
D IP(V a, V b) {
	return (a.real() * b.real() + a.imag() * b.imag());
}

// 外積 (Exterior Product) : a×b = |a||b|sinθ
D EP(V a, V b) {
	return (a.real() * b.imag() - a.imag() * b.real());
}

// 2直線の直交判定 : a⊥b <=> IP(a, b) = 0
B IsVecular(P a1, P a2, P b1, P b2) {
	return IP(a1-a2, b1-b2)==0.0;
}

// 2直線の平行判定 : a//b <=> EP(a, b) = 0
B IsParallel(P a1, P a2, P b1, P b2) {
	return EP(a1-a2, b1-b2)== 0.0;
}


// 点と直線の距離 (Distance of Point and Line)  //l1の構造 x座標 first<second y座標 first>second 右上 正 左下 負 一致の
D  DPL(P p,L l){
	V v1=(p-l.first);
	V v2=(l.second-l.first);
	return EP(v1,v2)/abs(v1);
}

// 三角形の領域判定 Teritory of Triangle 内部のみ
B TT(P p1,P p2,P p3,P p){
	L l1,l2,l3;
	l1=make_pair(p2,p3);
	l2=make_pair(p3,p1);
	l3=make_pair(p1,p2);

	if(sig(DPL(p1,l1))!=sig(DPL(p,l1)))
		return false;
	else if(sig(DPL(p2,l2))!=sig(DPL(p,l2)))
		return false;
	else if(sig(DPL(p3,l3))!=sig(DPL(p,l3)))
		return false;
	else
		return true;
}


//変数名 = 型 代入したいもの
//example : v1 = V(5.0,-3.0) p1=P(0.0,4.0)
int main(void){
	int n; 
	while(true){
		if(cin.eof())
			break;
		P point[4];	
		rep(j,4)
		cin >> point[j].real() >> point[j].imag() ;
		if (TT(point[0],point[1],point[2],point[3]))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <math.h>
using namespace std;
double helon(double x1,double y1,double x2,double y2,double x3,double y3){
	double a,b,c,s,area;
	a = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
	b = sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
	c = sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
	s = (a+b+c)/2;
	area = sqrt(s*(s-a)*(s-b)*(s-c));
	return area;
}

int main(){
	double e=0.0000000001;
	double x1,y1,x2,y2,x3,y3,xp,yp;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3>>xp>>yp){
		double s,s1,s2,s3;
		s = helon(x1,y1,x2,y2,x3,y3);
		s1 = helon(xp,yp,x1,y1,x2,y2);
		s2 = helon(xp,yp,x2,y2,x3,y3);
		s3 = helon(xp,yp,x3,y3,x1,y1);
		cout<<s<<" "<<s1<<" "<<s2<<" "<<s3<<endl;
		if(fabs(s1)<e || fabs(s2)<e || fabs(s3)<e)
			cout<<"NO"<<endl;
		else if(fabs(s-(s1+s2+s3))<e)
			cout<<"YES"<<endl;
		else
			cout<<"NO"<<endl;
		
	}
	return 0;
}

C++: #include <iostream>
#include <complex>
using namespace std;

typedef complex<double> Point;

double cross(Point a, Point b){
    return (conj(a)*b).imag();
}

int main(){
    Point V[3], P;
    while(!cin.eof()){
        for(int i=0; i<3; i++){
            double x, y; cin >> x >> y;
            V[i] = {x, y};
        }
        double x, y; cin >> x >> y;
        P = {x, y};
        
        int sum1 = 0, sum2 = 0;
        for(int i=0; i<3; i++){
            double x = cross(V[(i+1)%3]-V[i], (P-V[i]));
            sum1 += x<=0;
            sum2 += x>=0;
        }
        cout << (sum1==3 || sum2==3? "YES": "NO") << endl;
    }
    return 0;
}