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++: #define _USE_MATH_DEFINES
#include<iostream>
#include<sstream>
#include<cstdlib>
#include<cmath>
using namespace std;

class Biv {
private:
  void set(Biv v) {
    x = v.x; y = v.y;
  }
public:
  string toString() {
    stringstream ss;
    ss << "(" << x << ", " << y << ")";
    return ss.str();
  }
  double x, y;
  Biv(double xx, double yy) {
    x = xx; y = yy;
  }
  Biv() {
    x = 0; y = 0;
  }
  void operator=(Biv v) { set(v); }
  Biv operator-() {
    return Biv(-x, -y);
  }
  Biv operator+(Biv v) {
    return Biv(x + v.x, y + v.y);
  }
  Biv operator-(Biv v) {
    return *this + (-v);
  }
  Biv multiple(double k) {
    return Biv(k * x, k * y);
  }
  Biv operator+=(Biv v) {
    set(*this + v); return *this;
  }
  Biv operator-=(Biv v) {
    set(*this - v); return *this;
  }
  friend ostream& operator<<(ostream& os, const Biv& v);
  double length() {
    return sqrt(x * x + y * y);
  }
  double arg() {
    if (x == 0) { return (y < 0) ? - M_PI / 2: M_PI / 2; }
    double val = atan(y / x);
    return (val > 0)? val:(M_PI + val);
  }
};

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

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

class Ttm {
private:
  void set(Ttm m) {
    a = m.a; b = m.b; c = m.c; d = m.d;
  }
public:
  double a, b, c, d;
  string toString() {
    stringstream ss;
    ss << "[" << a << "," << b << "," << c << "," << d << "]";
    return ss.str();
  }
  Ttm(double aa, double bb, double cc, double dd) {
    a = aa; b = bb; c = cc; d = dd;
  }
  Ttm() {
    a = 0; b = 0; c = 0; d = 0;
  }
  void operator=(Ttm m) { set(m); }
  Ttm operator-() {
    return Ttm(-a, -b, -c, -d);
  }
  Ttm operator+(Ttm m) {
    return Ttm(a+m.a, b+m.b, c+m.c, d+m.d);
  }
  Ttm operator-(Ttm m) {
    return *this + (-m);
  }
  Ttm operator*(Ttm m) {
    return Ttm(a*m.a+b*m.c, a*m.b+b+m.d, c*m.a+d*m.c, c*m.d+d*m.d);
  }
  Biv operator*(Biv v) {
    return Biv(a * v.x + b * v.y, c * v.x + d * v.y);
  }
  Ttm multiple(double k) {
    return Ttm(k*a, k*b, k*c, k*d);
  }
  Ttm operator+=(Ttm m) {
    set(*this + m); return *this;
  }
  Ttm operator-=(Ttm m) {
    set(*this - m); return *this;
  }
};

Ttm Rotate(double t) {
  return Ttm(cos(t), -sin(t), sin(t), cos(t));
}

bool in(Biv a, Biv b, Biv c, Biv p) {
  b -= a;
  c -= a;
  p -= a;
  
  if (cross(b,p) * cross(c,p) >= 0) {
     /*cout << "cross(" << b.toString() << "," << p.toString()
      << ") * cross(" << c.toString() << "," << p.toString() << ") > 0" << endl;*/
    return false; }
  /*cout << (c - b).toString() << endl;*/
  double t = (c - b).arg();
  /*cout << t << " "<< Rotate(-t).toString() << endl;*/
  b = Rotate(-t) * b;
  c = Rotate(-t) * c;
  p = Rotate(-t) * p;
  /*cout << "c="<<c.toString() << " ,p=" <<p.toString()<<endl;*/

  return p.y > c.y;
}


int main() {
  Biv p1, p2, p3, pp;

  while(cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y >> pp.x >> pp.y) {
    bool yes = in(p1, p2, p3, pp);

    cout << ( yes ? "YES" : "NO") << endl;
  }
}

C++: #include <iostream>
#include <cmath>

double gaiseki(double[2], double[2]);

int main(){
	double triPoint1[2];	//三角形の点1
	double triPoint2[2];	//三角形の点2
	double triPoint3[2];	//三角形の点3
	double pPoint[2];		//点Pの座標

	while (std::cin >> triPoint1[0] >> triPoint1[1]
		>> triPoint2[0] >> triPoint2[1]
		>> triPoint3[0] >> triPoint3[1]
		>> pPoint[0] >> pPoint[1]){
		double vector1_2[2] = { triPoint2[0] - triPoint1[0], triPoint2[1] - triPoint1[1] };
		double vector1_p[2] = { pPoint[0] - triPoint1[0], pPoint[1] - triPoint1[1] };
		double vector2_3[2] = { triPoint3[0] - triPoint2[0], triPoint3[1] - triPoint2[1] };
		double vector2_p[2] = { pPoint[0] - triPoint2[0], pPoint[1] - triPoint2[1] };
		double vector3_1[2] = { triPoint1[0] - triPoint3[0], triPoint1[1] - triPoint3[1] };
		double vector3_p[2] = { pPoint[0] - triPoint3[0], pPoint[1] - triPoint3[1] };
		
		if ((gaiseki(vector1_2, vector1_p) > 0 && gaiseki(vector2_3, vector2_p) > 0 && gaiseki(vector3_1, vector3_p) > 0)
			|| (gaiseki(vector1_2, vector1_p) < 0 && gaiseki(vector2_3, vector2_p) < 0 && gaiseki(vector3_1, vector3_p) < 0)){
			std::cout << "YES" << std::endl;
		}
		else{
			std::cout << "NO" << std::endl;
		}
	}
	return 0;
}

double gaiseki(double vector1[2], double vector2[2]){
	return vector1[0] * vector2[1] - vector1[1] * vector2[0];
}

C++: #include <cstdio>
#include <iostream>
#include <complex>
#define rep(i,n) for(int i=0; i<(n); i++)
#define EPS 1e-10
using namespace std;

typedef complex<double> cd;

double s(cd a, cd b){
  return abs( a.real()*b.imag()-a.imag()*b.real() );
}

int main(){
  cd a[4];

  for(;;){
    rep(i,4){
      double x,y;
      if(scanf(" %lf %lf", &x,&y)==EOF)
        return 0;
      a[i]=cd(x,y);
    }
    
    if(abs(s(a[0]-a[3], a[1]-a[3])
           + s(a[1]-a[3], a[2]-a[3])
           + s(a[2]-a[3], a[0]-a[3])
           - s(a[1]-a[0], a[2]-a[0])) < EPS )
      printf("IN\n");
    else
      printf("OUT\n");
  }
  
  return 0;
}

C++: #include <cstdio>
#include <algorithm>
#define LOOP(index,times) for(int index=0;index<times;index++)
using namespace std;

int main(){

float x[3],y[3],xp,yp;

while(scanf("%f %f %f %f %f %f %f %f",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2],&xp,&yp) != EOF){

sort(x,x+3);
sort(y,y+3);

if(x[0] < xp && xp < x[2] && y[0] < yp && yp < y[2])
	printf("\nYES");
else
	printf("\nNO");

}
return 0;		
}