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 ;

#define pb(n) push_back(n)
#define fi first
#define se second
#define X real()
#define Y imag()
#define all(r) (r).begin(),(r).end()
#define gsort(st,en) sort((st),(en),greater<int>())
#define vmax(ary) *max_element(all(ary))
#define vmin(ary) *min_element(all(ary))
#define debug(x) cout<<#x<<": "<<x<<endl
#define fcout(n) cout<<fixed<<setprecision((n))
#define scout(n) cout<<setw(n)
#define vary(type,name,size,init) vector< type> name(size,init)

#define rep(i,n) for(int i = 0; i < (int)(n);++i)
#define REP(i,a,b) for(int i = (a);i < (int)(b);++i)
#define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it)
#define repa(n,array) for(auto &n :(array))

using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using dict = map<string,int>;
using comd = complex<double>;
using pii = pair<int,int> ;

constexpr int imax = ((1<<30)-1)*2+1 ;
constexpr int inf = 100000000;
constexpr double PI = acos(-1.0) ;
double eps = 1e-10 ;
const int dy[] = {-1,0,1,0};
const int dx[] = {0,-1,0,1};

inline bool value(int x,int y,int w,int h){
  return (x >= 0 && x < w && y >= 0 && y < h);
}

double CalcDist(comd p1, comd p2){
  return sqrt(pow(p1.X - p2.X,2.0) + pow(p1.Y -p2.Y,2.0));
}

template<typename T>
void Unique(vector<T> &v){
  sort(all(v));
  v.erase(all(v),v.end());
}

template<typename T>
T ston(string& str, T n){
  istringstream sin(str) ;
  T num ;
  sin >> num ;
  return num ;
}

void Ans(bool f){
  if(f) cout << "YES"<<endl;
  else cout << "NO"<<endl;
}

double EPS = 1e-10;
double add(double a, double b){
  if(abs(a+b) < EPS* (abs(a) + abs(b))) return 0;
  return a+b;
}
struct P{
  double x,y;
  P(){}
  P(double _x,double _y):x(_x),y(_y){}
  P operator + (P p){
    return P(add(x,p.x) ,add(y,p.y));
  }
  P operator - (P p){
    return P(add(x,-p.x) ,add(y,-p.y));
  }
  P operator * (double d){
    return P(x * d,y * d);
  }
  double norm(){
    return x*x + y*y;
  }
  double dot(P p){
    return add(x * p.x,y*p.y);
  }
  double det(P p){
    return add(x*p.y,-y*p.x);
  }
  double dist2(P p){
    return ((*this-p).x * (*this-p).x) + ((*this-p).y * (*this-p).y);
  }
  double GetSlope(P &p){
    P tmp = *this - p;
    return tmp.y/tmp.x;
  }
};
//???????????????????????¨?????????
bool on_seg(P p1,P p2,P q){
  return (p1-q).det(p2-q) == 0 && (p1-q).dot(p2-q) <= 0;
}

bool check(P p1,P p2,P p3, P p4){
  P a = p1 - p2,b = p3 - p2, p = p4 - p2;
  double theta1 = acos(a.dot(b)/(a.norm() * b.norm()));
  double thetap = acos(a.dot(p)/(a.norm() * p.norm()));
  return thetap <= theta1 ;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  double a,b,c,d,e,f,xp,yp;
  while(cin >> a >> b >> c >> d >> e >> f >> xp >> yp){
    bool flag = true;
    double acx = c-a,abx = e-a,acy = d-b,aby = f-b,apx = xp-a,apy = yp - b;
    P p1 = P(a,b),p2 = P(c,d),p3 = P(e,f),p4 = P(xp,yp);
    Ans(check(p1,p2,p3,p4) && check(p1,p3,p2,p4));
  }
  return 0;
}

C++: #include <iostream>
#include <math.h>
using namespace std;
double getCross( double x1, double y1, double x2, double y2 )
{
	return x1 * y2 - y1 * x2;
}
bool same( double a, double b )
{
	if ( a >= 0 && b >= 0 )
		return true;
	if ( a <= 0 && b <= 0 )
		return true;
	return false;
}
int main( void )
{
	double x1, y1, x2, y2, x3, y3, xp, yp;
	while ( cin >> x1 >> y1 >> x2 >> y2>> x3 >> y3 >> xp >> yp )
	{
		double a = getCross( xp-x1, yp-y1, xp-x2, xp-y2 );
		double b = getCross( xp-x2, yp-y2, xp-x3, yp-y3 );
		double c = getCross( xp-x3, yp-y3, xp-x1, yp-y1 );

		if ( same( a, b ) == same( b, c ) )
			cout << "YES" << endl;
		else
			cout << "NO" << endl;

	}
	return 0;
}

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

C++: #include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
#include <cmath>
#include <complex>
#include <map>
using namespace std;
 
#define rep(i,n) for(int i=0;i<int(n);++i)
 
static const double PI=6*asin(0.5);
typedef complex<double> P;
typedef long long ll;
static const double eps = 1e-8;
 
double x[3],y[3];
double xp,yp;
 
double dist(P a,P b){
    return (sqrt((real(a)-real(b))*(real(a)-real(b))+(imag(a)-imag(b))*(imag(a)-imag(b))));
}
 
double tri_pro(P a,P b,P c){
    double aa,bb,cc;
    aa = dist(b,c);
    bb = dist(c,a);
    cc = dist(a,b);
    double s = (aa+bb+cc)/2.0;
    return sqrt(s*(s-aa)*(s-bb)*(s-cc));
}
 
 
int main(){
    //P a(0.0,0.0),b(4.0,0.0),c(4.0,2.0);
    //cout<<tri_pro(a,b,c)<<endl;
    
    
    
    while(cin>>x[0]>>y[0]){
        rep(i,2) cin>>x[i+1]>>y[i+1];
        cin>>xp>>yp;
        P a(x[0],y[0]),b(x[1],y[1]),c(x[2],y[2]);
        P p(xp,yp);
        double sa,sb,sc;
        sa = tri_pro(b,c,p);
        sb = tri_pro(c,a,p);
        sc = tri_pro(a,b,p);
        double s = tri_pro(a,b,c);
        //cout<<"s="<<s<<"\nsa sb sc "<<sa<<" "<<sb<<" "<<sc<<endl;
        if((int)(s*10000000)-(int)((sa+sb+sc)*10000000)==0) cout<<"YES\n";
        else cout<<"NO\n";
    }
    
    return 0;
}