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 sqrt(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 theta2 = acos(b.dot(a)/(a.norm() * b.norm()));
  double thetap = acos(a.dot(p)/(a.norm() * p.norm()));
  double thetaq = acos(b.dot(p)/(a.norm() * p.norm()));
  //   debug(theta1);
  //   debug(theta2);
  //   debug(thetap);
  //   debug(thetaq);
  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) && check(p3,p1,p2,p4));
  }
  return 0;
}

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

typedef complex<double> P;

#define EPS (1e-10)

double area(double a, double b, double c){
  double s = (a + b + c) / 2;
  return sqrt(s*(s-a)*(s-b)*(s-c));
}

int main(void){
  double x1, x2, x3, y1, y2, y3, xp, yp;
  while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){
    P a = P(x1, y2), b = P(x2, y2), c = P(x3, y3), p = P(xp, yp);
    double ab = abs(a - b), bc = abs(b - c), ca = abs(c - a);
    double ap = abs(a - p), bp = abs(b - p), cp = abs(c - p);
    double abc = area(ab, bc, ca);
    double abp = area(ab, ap, bp);
    double acp = area(ca, ap, cp);
    double bcp = area(bc, bp, cp);
    double diff = (abp + acp + bcp) - abc;

    if(diff < EPS) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  return 0;
}

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

typedef complex<double> P;

#define EPS (1e-8)

double area(double a, double b, double c){
  double s = (a + b + c) / 2;
  return sqrt(s*(s-a)*(s-b)*(s-c));
}

int main(void){
  double x1, x2, x3, y1, y2, y3, xp, yp;
  while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){
    P a = P(x1, y2), b = P(x2, y2), c = P(x3, y3), p = P(xp, yp);
    double ab = abs(a - b), bc = abs(b - c), ca = abs(c - a);
    double ap = abs(a - p), bp = abs(b - p), cp = abs(c - p);
    double abc = area(ab, bc, ca);
    double abp = area(ab, ap, bp);
    double acp = area(ca, ap, cp);
    double bcp = area(bc, bp, cp);
    double diff = (abp + acp + bcp) - abc;

    if(diff < EPS) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  return 0;
}

C++: #include <iostream>
#include <stack>
using namespace std;
double a,b,c;//ax+by+c=0
double x[4],y[4];//p,1,2,3
void make_line(double x1,double y1,double x2,double y2){
	if(x1!=x2&&y1!=y2){
		a=(y1-y2)/(x1-x2);
		b=-1;
		c=-a*x1+y1;
	}else if(x1==x2){
		a=1;
		b=0;
		c=-x1;
	}else if(y1==y2){
		a=0;
		b=1;
		c=-y1;
	}
	return;
}
bool check(int p,int q,int r){
	make_line(x[p],y[p],x[q],y[q]);//line pq
	if((a*x[r]+b*y[r]+c)*(a*x[0]+b*y[0]+c)<=0)return false;
	return true;
}

int main()
{
	while(cin>>x[1]>>y[1]>>x[2]>>y[2]>>x[3]>>y[3]>>x[0]>>y[0]){
		bool ans=true;
		ans&=check(1,2,3);
		ans&=check(2,3,1);
		ans&=check(3,1,2);
		printf(ans?"YES\n":"NO\n");
	}
    return 0;
}