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 <bits/stdc++.h>
using namespace std;

typedef ostringstream OSS; typedef istringstream ISS;
typedef long long LL;
typedef pair<int, int> PII;  typedef pair<LL, LL> PLL;
typedef vector<int>    VI;   typedef vector<VI>   VVI;   typedef vector<VVI>   VVVI;
typedef vector<LL>     VLL;  typedef vector<VLL>  VVLL;  typedef vector<VVLL>  VVVLL;
typedef vector<double> VD;   typedef vector<VD>   VVD;   typedef vector<VVD>   VVVD;
typedef vector<string> VS;   typedef vector<VS>   VVS;   typedef vector<VVS>   VVVS;
typedef vector<bool>   VB;   typedef vector<VB>   VVB;   typedef vector<VVB>   VVVB;
typedef vector<PII>    VPII; typedef vector<VPII> VVPII; typedef vector<VVPII> VVVPII;
typedef vector<PLL>    VPLL; typedef vector<VPLL> VVPLL; typedef vector<VVPLL> VVVPLL;

typedef unsigned int  UI;
typedef vector<UI>    VUI;
typedef vector<VUI>   VVUI;

#define fst first
#define snd second
// #define Y first
// #define X second
#define MP make_pair
#define PB push_back
#define EB emplace_back 
#define ALL(x)  (x).begin(),(x).end()
#define RALL(x) (x).rbegin(),(x).rend()
#define RANGEBOX(x,y,maxX,maxY) (0 <= (x) && 0 <= (y) && (x) < (maxX) && (y) < (maxY))
#define RANGE(x, l, r) ((l) <= (x) && (x) <= (r))
#define rep(i, N)  for (int i = 0; i < (int)(N); i++)
#define rrep(i, N) for (int i = N - 1; i >= 0; i--)
#define REP(i, init, N)  for (int i = (init); i < (int)(N); i++)
#define RREP(i, N, last) for (int i = (init - 1); i >= last; i--)
#define MAXUD(orig, target) orig = max(orig, target)
#define MINUD(orig, target) orig = min(orig, target)
#define DUMP( x ) cerr << #x << " = " << ( x ) << endl

template < typename T > inline T fromString(const string &s) { T res; ISS iss(s); iss >> res; return res; };
template < typename T > inline string toString(const T &a)   { OSS oss; oss << a; return oss.str(); };

template<typename T=int> inline void dump(vector<T> vs, bool ent=false) { rep(i, vs.size()) cout << vs[i] << (i+1==vs.size() ? '\n' : ' '); if (ent) cout << endl; }
template<typename T = int> inline void dump(vector<vector<T>> vs, bool ent = false) { rep(i, vs.size()) dump<T>(vs[i]); if (ent) cout << endl; }

const int    INF  = 0x3f3f3f3f;
const LL     INFL = 0x3f3f3f3f3f3f3f3fLL;
const double DINF = 0x3f3f3f3f;
const int    DX[] = {1,  0, -1, 0};
const int    DY[] = {0, -1,  0, 1};
const double EPS  = 1e-12;
// const double PI   = acos(-1.0);
// lambda: [](T1 x)->T2{return y;}
// simple lambda: [](T x){return x;}

#define X real()
#define Y imag()

typedef complex<double> P;

// a = b
bool eq(double a, double b) {
    return abs(a - b) < EPS;
}

// ?????¢
double distPP(P a, P b) {
    return abs(a - b);
}

// ??????????????¬???
double heron(double a, double b, double c) {
    double s = (a + b + c) / 2.;
    return sqrt(s * (s - a) * (s - b) * (s - c));
}

double heron(P a, P b, P c) {
    return heron(distPP(a, b), distPP(b, c), distPP(c, a));
}

// ????§???¢??¨??????????????????
bool inTriangle(P a, P b, P c, P p) {
    double s1 = heron(a, b, c);
    double s2 = heron(p, b, c) + heron(a, p, c) + heron(a, b, p);
    return eq(s1, s2);
}

int main(void) {
    double x1, y1, x2, y2, x3, y3, xp, yp;
    while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp) {
        P a(x1, y1);
        P b(x2, y2);
        P c(x3, y3);
        P p(xp, yp);
        cout << (inTriangle(a, b, c, p) ? "YES" : "NO") << endl;
    }


    return 0;
}

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

using namespace std;

double get2pDist(double, double, double, double);
double getplDist(double, double, double, double, double, double);
double getTriangle(double, double, double, double, double, double);

int main(){
	double x1, y1, x2, y2, x3, y3, xp, yp;
	while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){
		double S = getTriangle(x1, y1, x2, y2, x3, y3);
		double s =
			getTriangle(x1, y1, x2, y2, xp, yp)
			+ getTriangle(x2, y2, x3, y3, xp, yp)
			+ getTriangle(x3, y3, x1, y1, xp, yp);
		abs(S - s) == 0 ? cout << "YES" << endl : cout << "NO" << endl;
	}
	return 0;
}

double get2pDist(double x1, double y1, double x2, double y2){
	return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));	
}

double getplDist(double x, double y, double x1, double y1, double x2, double y2){
	double a, b, c;
	a = y1 - y2;
	b = x2 - x1;
	c = x1 * y2 - x2 * y1;
	return abs(a * x + b * y + c) / sqrt(a * a + b * b);
}

double getTriangle(double x1, double y1, double x2, double y2, double x3, double y3){
	return (get2pDist(x1, y1, x2, y2)
	 * getplDist(x3, y3, x1, y1, x2, y2)) / 2;
}

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; };

point sub(const point& a, const point& b){
  point ret;
  ret.x = a.x - b.x;
  ret.y = a.y - b.y;
  return ret;
}

int solve(point a, point b, point c, point p){
  point ab = sub(b, a), bp = sub(p, b);
  point bc = sub(c, b), cp = sub(p, c);
  point ca = sub(a, c), ap = sub(p, a);

  double c1 = ab.x * bp.y - ab.y * bp.x;
  double c2 = bc.x * cp.y - bc.y * cp.x;
  double c3 = ca.x * ap.y - ca.y * ap.x;

  if((c1 > 0 && c2 > 0 && c3 > 0) || (c1 < 0 && c2 < 0 && c3 < 0)) 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 = y1; a.y = x1;
    b.x = y2; b.y = x2;
    c.x = y3; c.y = x3;
    P.x = yp; P.y = xp;

    if(solve(a, b, c, P)) puts("YES");
    else puts("NO");
  }
  return 0;
}