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 <stdio.h>

int main(void)
{
  double x1,y1,x2,y2,x3,y3,xp,yp;
  double a,b,c;
  
  while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &xp, &yp)!=EOF){
  
    a = (x1-xp)*(y2-yp)-(x2-xp)*(y1-yp);
    b = (x2-xp)*(y3-yp)-(x3-xp)*(y2-yp);
    c = (x3-xp)*(y1-yp)-(x1-xp)*(y3-yp);
  
  
    if( (a>0&&b>0&&c>0) || (a<0&&b<0&&c<0) ){
      printf("YES\n");
    }else{
      printf("NO\n");
    }
  }
  return 0;
  
}

C++: #include<cstdio>
#include<cstring>
#include<iostream>
#include<cstdlib>
#include<cmath>
using namespace std;
int CCross(double x1,double y1,double x2,double y2,double x3,double y3,double x4,double y4){
	double S,T,D;	//	一時変数を宣言

	//	分母を先に計算。計算量を減らすため、分子は後で行う。
	D = (x3-x1) * (y4-y1) - (y3-y1) * (x4-x1);
	
	//	D の符号に応じて分岐
	if(D < 0){
	  S = (y4-y1)*(x2-x1) - (x4-x1)*(y2-y1);
	  T = (x3-x1)*(y2-y1) - (y3-y1)*(x2-x1);
	  
	  return S < 0 && T < 0 && (S+T)/D > 1 ;
	}
	else if(D > 0){
	  S = (y4-y1)*(x2-x1) - (x4-x1)*(y2-y1);
	  T = (x3-x1)*(y2-y1) - (y3-y1)*(x2-x1);
	    
	    return S > 0 && T > 0 && (S+T)/D > 1 ;
	}
	
	//	D = 0 の時には、点が線分の上かどうかを判定する。
	return 0;
}
double GetLen(double x1,double y1,double x2,double y2){
  double X1=min(x2,x1),X2=max(x2,x1);
  double Y1=min(y2,y1),Y2=max(y2,y1);
  return sqrt((Y2-Y1)*(Y2-Y1)+(X2-X1)*(X2-X1));
}
main(){
  double x1,y1,x2,y2,x3,y3,xp,yp; 
  while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&xp,&yp)!=EOF){
    double R;
    double a,b,c;
    if(CCross(x1,y1,xp,yp,x2,y2,x3,y3) ||
       CCross(x2,y2,xp,yp,x3,y3,x1,y1) ||
       CCross(x3,y3,xp,yp,x1,y1,x2,y2) ){
       printf("NO\n");
    }
    else printf("YES\n");
  }
}

C++: #include<stdio.h>
int main(){
	double x1,x2,x3,x4,y1,y2,y3,y4;
	while(~scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4)){
		bool ok1=true;
		bool ok2=true;
		if((x2-x1)*(y4-y1)-(x4-x1)*(y2-y1)<0)ok1=false;
		else ok2=false;
		if((x3-x2)*(y4-y2)-(x4-x2)*(y3-y2)<0)ok1=false;
		else ok2=false;
		if((x1-x3)*(y4-y3)-(x4-x3)*(y1-y3)<0)ok1=false;
		else ok2=false;
		printf((ok1||ok2)?"YES\n":"NO\n");
	}
}

C++: #include <complex>
#include <stdio.h>
#include <math.h>
using namespace std;

// _ÀWð^Æ·é
typedef complex<double> P;
// ÎÌè`
#define PI 3.1415926535898

// e·éë·Ã
#define EPS (1e-10)
//
#define X real()
#define Y imag()
	
// Op`NX
class Triangle{

private:
	//Op`ÌR_ÌÀW
	P a, b, c;
	//Op`ÌRÓÌ·³
	double edgeA,edgeB,edgeC;
	//Op`ÌRpÌå«³(WA)
	double angleA,angleB,angleC;
	//Op`ÌÊÏ
	double s;
	//]·è©çRÂÌpxðßéÖ
	double LawOfCosines(double a,double b, double c){
		return acos( (b*b+c*c-a*a) / (2.0*b*c) );
	}
	bool equal(double a, double b){//QÂÌdouble^Ìlªµ¢©Ç¤©
		return (fabs( a-b ) < EPS)? true : false ;
	}
	bool checkRightAngle(double a){//pª¼p©»è·é
		return ( fabs( a-(PI/2.0) ) < EPS )? true : false;
	}

public:
	//RXgN^(RÂÌ_ÆÓÆpxðú»)
	Triangle(P p1, P p2, P p3){
		a = p1;
		b = p2;
		c = p3;
		edgeB = abs(c-a);
		edgeA = abs(b-c);
		edgeC = abs(a-b);
		angleA = LawOfCosines(edgeA,edgeB,edgeC);
		angleB = LawOfCosines(edgeB,edgeC,edgeA);
		angleC = LawOfCosines(edgeC,edgeA,edgeB);
		double hoge;
		hoge = (edgeA+edgeB+edgeC)/2.0;
		s = sqrt(hoge*(hoge-edgeA)*(hoge-edgeB)*(hoge-edgeC));
	}
	
	
	double getAx(){//_AÌXÀWðÔ·
		return a.X;
	}
	double getAy(){//_AÌYÀWðÔ·
		return a.Y;
	}
	double getBx(){//_BÌXÀWðÔ·
		return b.X;
	}
	double getBy(){//_BÌYÀWðÔ·
		return b.Y;
	}
	double getCx(){//_CÌXÀWðÔ·
		return c.X;
	}
	double getCy(){//_CÌYÀWðÔ·
		return c.Y;
	}
	double getEdgeA(){//ÓAÌ·³ðÔ·
		return edgeA;
	}
	double getEdgeB(){//ÓBÌ·³ðÔ·
		return edgeB;
	}
	double getEdgeC(){//ÓCÌ·³ðÔ·
		return edgeC;
	}
	double getAngleA(){//pAÌpx(WA)ðÔ·
		return angleA;
	}
	double getAngleB(){//pBÌpx(WA)ðÔ·
		return angleB;
	}
	double getAngleC(){//pCÌpx(WA)ðÔ·
		return angleC;
	}
	double getArea(){//Op`ÌÊÏðÔ·
		return s;
	}
	double circumscribedCircleRadius(){//OÚ~Ì¼aðÔ·
		return ( edgeA / sin(angleA) / 2.0 );
	}
	double circumscribedCircleX(){//OS(OÚ~ÌS)ÌXÀWðÔ·
		double A = sin(2.0*angleA);
		double B = sin(2.0*angleB);
		double C = sin(2.0*angleC);
		return ( (a.X * A + b.X * B + c.X * C) / (A+B+C) );
	}
	double circumscribedCircleY(){//OS(OÚ~ÌS)ÌYÀWðÔ·
		double A = sin(2.0*angleA);
		double B = sin(2.0*angleB);
		double C = sin(2.0*angleC);
		return ( (a.Y * A + b.Y * B + c.Y * C) / (A+B+C) );
	}
	double incenterRadius(){//àÚ~Ì¼aðÔ·
		return ( (2.0*s) / (edgeA+edgeB+edgeC) );
	}
	double incenterX(){//àS(àÚ~ÌS)ÌXÀWðÔ·
		return ( (edgeA*a.X+edgeB*b.X+edgeC*c.X) / (edgeA+edgeB+edgeC) );
	}
	double incenterY(){//àS(àÚ~ÌS)ÌYÀWðÔ·
		return ( (edgeA*a.Y+edgeB*b.Y+edgeC*c.Y) / (edgeA+edgeB+edgeC) );
	}
	double centerOfGravityX(){//dSÌXÀWðÔ·
		return ( (a.X+b.X+c.X) / 3.0 );
	}
	double centerOfGravityY(){//dSÌYÀWðÔ·
		return ( (a.Y+b.Y+c.Y) / 3.0 );
	}
	bool checkRightTriangle(){//¼pOp`©Ç¤©»è·é
		if(checkRightAngle(angleA)||checkRightAngle(angleB)||checkRightAngle(angleC)){
			return true;
		}else{
			return false;
		}
	}
	bool checkIsoscelesTriangle(){//ñÓOp`©»è·é 
		if( equal(angleA,angleB) || equal(angleB,angleC) || equal(angleC,angleA) ){
			return true;
		}else{
			return false;
		}
	}
	bool checkEquilateralTriangle(){//³Op`©»è·é 
		if( equal(edgeA,edgeB) && equal(edgeB,edgeC) && equal(edgeC,edgeA)){
			return true;
		}else{
			return false;
		}
	}
};

int main(){
	int n;
	double x1,y1,x2,y2,x3,y3,xp,yp;
	
	while ( scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&xp,&yp) != EOF ){
		P a(x1,y1), b(x2,y2), c(x3,y3), p(xp,yp);
		Triangle Tr1(a,b,p);
		Triangle Tr2(b,c,p);
		Triangle Tr3(c,a,p);
		double pAngle = Tr1.getAngleC() + Tr2.getAngleC() + Tr3.getAngleC();
		if( fabs( pAngle - (2.0*PI) ) < EPS ){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
	
	return 0;
}

C++: #include <complex>
#include <cstdio>
using namespace std;
typedef complex<double> P;
double cross(const P& a, const P& b) {
	return imag(conj(a)*b);
}
bool in_triangle(const P& p1,const P& p2,const P& p3,const P& p){
	return cross(p2-p1,p-p1)>0 && cross(p3-p2,p-p2)>0 && cross(p1-p3,p-p3)>0;
}
int main(){
	double x1,y1,x2,y2,x3,y3,x,y;
	for(;~scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x,&y);){
		P p1(x1,y1),p2(x2,y2),p3(x3,y3),p(x,y);
		bool in=in_triangle(p1,p2,p3,p)||in_triangle(p2,p1,p3,p);
		puts(in?"YES":"NO");
	}
}