Go: package main

import (
        "fmt"
)

func main() {
        var x1, y1, x2, y2, x3, y3, px, py float64
        var oax, oay, obx, oby, opx, opy float64
        var det float64
        var s, t float64

        for {
                _, err := fmt.Scanf("%f %f %f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3, &px, &py)
                if err != nil {
                        break
                }
                oax = x2 - x1
                oay = y2 - y1
                obx = x3 - x1
                oby = y3 - y1
                opx = px - x1
                opy = py - y1
                det = oax*oby - obx*oay

                if det == 0 {
                        fmt.Printf("NO\n")
                } else {
                        s = (oby*opx - obx*opy) / det
                        t = (oax*opy - oay*opx) / det

                        if (s+t < 1 && s > 0 && t > 0) {
                                fmt.Printf("YES\n")
                        } else {
                                fmt.Printf("NO\n")
                        }
                }
        }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <cstring>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>

using namespace std;

static const double EPS = 1e-9;
typedef long long ll;
typedef pair<int, int> paii;
typedef complex<double> P;

double ccw(P& p1, P& p2, P& p3)
{
	return ((p2.real() - p1.real())*(p3.imag() - p1.imag()) 
				- (p2.imag() - p1.imag())*(p3.real() - p1.real())) > 0;
}// ccw>0 ...ccw, ccw=0 ...colinear, ccw<0 ...cw

int main()
{
	double x, y;
	P p1, p2, p3, px;
	
	while(cin >> x, !cin.eof())
	{
		cin >> y;
		p1 = P(x, y);
		cin >> x >> y;
		p2 = P(x, y);
		cin >> x >> y;
		p3 = P(x, y);
		cin >> x >> y;
		px = P(x, y);
		
		if(( ccw(p1, p2, px) > 0 && ccw(p2, p3, px) > 0 && ccw(p3, p1, px) > 0)
			||( ccw(p1, p2, px) < 0 && ccw(p2, p3, px) < 0 && ccw(p3, p1, px) < 0))
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

class D3
{
public:
	double x;
	double y;
	double z;

	//?????????????????????
	D3 ( double x_ = 0.0 , double y_ = 0.0 , double z_ = 0.0 )
	{
		x = x_;
		y = y_;
		z = z_;
	}

	//??????
	D3 Cross_product ( D3 partner )
	{
		D3 ret ( y*partner.z - z*partner.y , z*partner.x - x*partner.z , x*partner.y - y*partner.x );
		return ret;
	}

	//??????
	double Inner_product ( D3 partner )
	{
		return x*partner.x + y*partner.y + z*partner.z;
	}

	//?????????????????????????????????
	D3 Make_vector ( D3 partner )
	{
		D3 ret ( partner.x - x , partner.y - y , partner.z - z );
		return ret;
	}

	//???????§????2????????????????????¢???????±???????
	double S_vec ( D3 A , D3 B )
	{
		D3 G;
		G = A.Cross_product ( B );
		return sqrt ( G.Inner_product ( G ) ) / 2;
	}

	//??????????????¢???????±???????
	double S_point ( D3 A , D3 B , D3 C )
	{
		return S_vec ( A.Make_vector ( B ) , A.Make_vector ( C ) );
	}

	//???????§????3????????????????????????????±???????
	double V_vec ( D3 A , D3 B , D3 C )
	{
		D3 G;
		G = A.Cross_product ( B );
		return G.Inner_product ( C ) / 6;
	}

	//4???????????????????±???????
	double V_point ( D3 A , D3 B , D3 C , D3 D )
	{
		return V_vec ( A.Make_vector ( B ) , A.Make_vector ( C ) , A.Make_vector ( D ) );
	}

	D3 operator+( D3 partner )
	{
		return D3 ( x + partner.x , y + partner.y , z + partner.z );
	}

	D3 operator-( D3 partner )
	{
		return D3 ( x - partner.x , y - partner.y , z - partner.z );
	}

	D3 operator*( D3 partner )
	{
		return D3 ( x * partner.x , y * partner.y , z * partner.z );
	}

	D3 operator/( D3 partner )
	{
		return D3 ( x / partner.x , y / partner.y , z / partner.z );
	}

	D3 operator*( double d )
	{
		return D3 ( x * d , y * d , z * d );
	}

	D3 operator/( double d )
	{
		return D3 ( x / d , y / d , z / d );
	}

	bool operator==( D3 partner )
	{
		return x == partner.x&&y == partner.y&&z == partner.z;
	}

	double length ()
	{
		return sqrt ( x*x + y*y + z*z );
	}

	//???????????????????????????
	//????????¨???
	D3 Unit_vec ()
	{
		return D3 ( *this ) / ( *this ).length ();
	}

	//????????????????????????
	D3 Inverse_vec ()
	{
		return D3 ( *this )*-1;
	}

	//?????´????????????
	bool Vertical ( D3 partner )
	{
		return ( *this ).Inner_product ( partner ) == 0;
	}

	//??????????????????
	bool Parallel ( D3 partner )
	{
		return ( *this ).Unit_vec () == partner.Unit_vec () || ( *this ).Unit_vec ().Inverse_vec () == partner.Unit_vec ();
	}

};

int main ()
{
	double x1 , y1 , x2 , y2 , x3 , y3 , xp , yp;
	while( cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp )
	{
		D3 X ( x1 , y1 ) , Y ( x2 , y2 ) , Z ( x3 , y3 ) , P ( xp , yp ) , calc;
		if( calc.S_point ( X , Y , Z ) - ( calc.S_point ( X , Y , P ) + calc.S_point ( X , Z , P ) + calc.S_point ( Z , Y , P ) ) < 1e-9 )
		{
			cout << "YES" << endl;
		} else
		{
			cout << "NO" << endl;
		}
	}

}

C++: #include <stdio.h>
#include <math.h>

using namespace std;

//I searched this method by WEB.

int main(){
	double x1,x2,x3,y1,y2,y3,xp,yp;
	double calc1,calc2,calc3;

	while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&xp,&yp)!=EOF){
		calc1 = (x1-xp)*(y2-yp)-(y1-yp)*(x2-xp);

		calc2 = (x3-xp)*(y1-yp)-(y3-yp)*(x1-xp);

		calc3 = (x2-xp)*(y3-yp)+(y2-yp)*(x2-xp);

		if((calc1>0&&calc2>0&&calc3>0) || (calc1<0&&calc2<0&&calc3<0)){
			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 real()
#define Y 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());
}

// 点の進行方向について 3
int ccw(P a, P b, P c) {              //点aと点bが与えられた問いに
  b -= a; c -= a;
  if (EP(b, c) > 0)   return +1;      // counter clockwise
  if (EP(b, c) < 0)   return -1;      // clockwise
  if (IP(b, c) < 0)     return +2;    // c--a--b on line
  if (norm(b) < norm(c)) return -2;   // a--b--c on line
  return 0;                           // a--c--b on line  aとbの線分判定はこれ
}

int main(void){
	while(true){
		if(cin.eof())
			break;
		P point[4];	
		int tmp;
		rep(j,4)
		cin >> point[j].X >> point[j].Y;
		bool flag=true;
		for(int i=0;i<3;i++)
			if(ccw(point[i%3],point[(i+1)%3],point[(i+2)%3])!=ccw(point[i%3],point[(i+1)%3],point[3]))
				flag=false;
		if(flag)
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}
	return 0;
}