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 <iostream>
#include <complex>
#include <vector>
#include <algorithm>
#include <assert.h>
using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;
typedef P point;
namespace std {
  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }
}
double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
  return real(conj(a)*b);
}

struct L : public vector<P> {
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};

typedef vector<P> G;

struct C {
  P p; double r;
  C(const P &p, double r) : p(p), r(r) { }
};

int ccw(P a, P b, P c) {
  b -= a; c -= a;
  if (cross(b, c) > 0)   return +1;       // counter clockwise
  if (cross(b, c) < 0)   return -1;       // clockwise
  if (dot(b, c) < 0)     return +2;       // c--a--b on line
  if (norm(b) < norm(c)) return -2;       // a--b--c on line
  return 0;
}

bool intersectLL(const L &l, const L &m) {
  return abs(cross(l[1]-l[0], m[1]-m[0])) > EPS || // non-parallel
         abs(cross(l[1]-l[0], m[0]-l[0])) < EPS;   // same line
}
bool intersectLS(const L &l, const L &s) {
  return cross(l[1]-l[0], s[0]-l[0])*       // s[0] is left of l
         cross(l[1]-l[0], s[1]-l[0]) < EPS; // s[1] is right of l
}
bool intersectLP(const L &l, const P &p) {
  return abs(cross(l[1]-p, l[0]-p)) < EPS;
}
bool intersectSS(const L &s, const L &t) {
  return ccw(s[0],s[1],t[0])*ccw(s[0],s[1],t[1]) <= 0 &&
         ccw(t[0],t[1],s[0])*ccw(t[0],t[1],s[1]) <= 0;
}
bool intersectSP(const L &s, const P &p) {
  return abs(s[0]-p)+abs(s[1]-p)-abs(s[1]-s[0]) < EPS; // triangle inequality
}

P projection(const L &l, const P &p) {
  double t = dot(p-l[0], l[0]-l[1]) / norm(l[0]-l[1]);
  return l[0] + t*(l[0]-l[1]);
}

/* Maybe include bugs [p + 2.0]<=this */
P reflection(const L &l, const P &p) {
  return p + 2.0 * (projection(l, p) - p);
}
double distanceLP(const L &l, const P &p) {
  return abs(p - projection(l, p));
}
double distanceLL(const L &l, const L &m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m[0]);
}
double distanceLS(const L &l, const L &s) {
  if (intersectLS(l, s)) return 0;
  return min(distanceLP(l, s[0]), distanceLP(l, s[1]));
}
double distanceSP(const L &s, const P &p) {
  const P r = projection(s, p);
  if (intersectSP(s, r)) return abs(r - p);
  return min(abs(s[0] - p), abs(s[1] - p));
}
double distanceSS(const L &s, const L &t) {
  if (intersectSS(s, t)) return 0;
  return min(min(distanceSP(s, t[0]), distanceSP(s, t[1])),
             min(distanceSP(t, s[0]), distanceSP(t, s[1])));
}
P crosspoint(const L &l, const L &m) {
  double A = cross(l[1] - l[0], m[1] - m[0]);
  double B = cross(l[1] - l[0], l[1] - m[0]);
  if (abs(A) < EPS && abs(B) < EPS) return m[0]; // same line
  if (abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m[0] + B / A * (m[1] - m[0]);
}

vector<point> convex_hull(vector<point> ps) {
  int n = ps.size(), k = 0;
  sort(ps.begin(), ps.end());
  vector<point> ch(2*n);
  for (int i = 0; i < n; ch[k++] = ps[i++]) // lower-hull
    while (k >= 2 && ccw(ch[k-2], ch[k-1], ps[i]) <= 0) --k;
  for (int i = n-2, t = k+1; i >= 0; ch[k++] = ps[i--]) // upper-hull
    while (k >= t && ccw(ch[k-2], ch[k-1], ps[i]) <= 0) --k;
  ch.resize(k-1);
  return ch;
}

int main(){
	P t;
	while(1){
		vector<P> data;
		for(int i=0;i<4;i++){
			if( !(cin >> t.real() >> t.imag()))return 0;
			else data.push_back(t);
		}
		if(convex_hull(data).size()!=4){
			if(
				(convex_hull(data)[0] != data[3])&&
				(convex_hull(data)[1] != data[3])&&
				(convex_hull(data)[2] != data[3])
			){
				cout << "YES" << endl;
			}else{
				cout << "NO" << endl;
			}
		}else{
			cout << "NO" << endl;
		}
	}
};

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

#define EPS (1e-8)

double area(double xa, double ya, double xb, double yb, double xc, double yc){
  double s, a, b, c;
  a = sqrt((xa - xb) * (xa - xb) + (ya - yb) * (ya - yb));
  b = sqrt((xb - xc) * (xb - xc) + (yb - yc) * (yb - yc));
  c = sqrt((xc - xa) * (xc - xa) + (yc - ya) * (yc - ya));
  s = (a + b + c) / 2;
  return sqrt(s * (s - a) * (s - b) * (s - c));
}

int main(void){
  double x1, y1, x2, y2, x3, y3, xp, yp;
  while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){
    double abc, abp, bcp, cap;
    abc = area(x1, y1, x2, y2, x3, y3);
    abp = area(x1, y1, x2, y2, xp, yp);
    bcp = area(xp, yp, x2, y2, x3, y3);
    cap = area(x1, y1, xp, yp, x3, y3);
    if(fabs(abc - (abp + bcp + cap)) <= EPS){
      cout << "YES" << endl;
    }else{
      cout << "NO" << endl;
    }
  }
  return 0;
}

C++: #include <iostream>
using namespace std;
#define f(a,b) ((x[i]-x[(i+1)%3])*(b-y[i])-(y[i]-y[(i+1)%3])*(a-x[i]))
int main(){double x[4],y[4];while(cin>>x[0]>>y[0]){for(int i=1;i<4;i++) cin>>x[i]>>y[i];bool f=false;for(int i=0;i<3;i++){if(f(x[(i+2)%3],y[(i+2)%3])*f(x[3],y[3])<0){f = true;break;}}if(f) cout<<"NO\n";else cout<<"YES\n";}return 0;}