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) && check(p3,p1,p2,p4));
  }
  return 0;
}

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

int main(){
	double x1, y1, x2, y2, x3, y3, xp, yp;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3>>xp>>yp){
		double sall = (x1-x2)*(y1+y2) + (x2-x3)*(y2+y3) + (x3-x1)*(y3+y1);
		double s1 = (x1-x2)*(y1+y2) + (x2-xp)*(y2+yp) + (xp-x1)*(yp+y1);
		double s2 = (x1-xp)*(y1+yp) + (xp-x3)*(yp+y3) + (x3-x1)*(y3+y1);
		double s3 = (xp-x2)*(yp+y2) + (x2-x3)*(y2+y3) + (x3-xp)*(y3+yp);
		if(abs(sall) == abs(s1)+abs(s2)+abs(s3)){
			cout<<"YES"<<endl;
		} else {
			cout<<"NO"<<endl;
		}
	}
}

C++: //template
//include-------------------------------------
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<cmath>
#include<map>
#include<stack>

using namespace std;

//typedef--------------------------------------
typedef vector<int> VI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

#define MP make_pair

//repetition-----------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)

//constant-------------------------------------
const double PI = acos(-1.0);

//cout,cin-------------------------------------
#define COUT(x) cout<<(x)<<endl
#define CIN(x) cin>>(x)

int main(){

	double x1, y1, x2, y2, x3, y3, xp, yp;
	while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){

		//A点を原点に移動
		x2 -= x1; y2 -= y1;
		x3 -= x1; y3 -= y1;
		xp -= x1; yp -= y1;

		double k1, k2;
		k2 = (yp - (xp / x2)*y2) / (y3 - (x3 / x2)*y2);
		k1 = (xp - k2*x3) / x2;

		if ((k1 > 0) && (k2 > 0) && (k1 + k2 < 1)) COUT("YES");
		else COUT("NO");
	}

	return 0;

}

C++: #include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;
using ll = long long;
typedef complex<double> xy_t;

double x[4], y[4];

double dot_product(xy_t a, xy_t b)
{
    return (conj(a) * b).real();
}

double cross_product(xy_t a, xy_t b)
{
    return (conj(a) * b).imag();
}

int main()
{
    while (true)
    {
        rep(i, 4) cin >> x[i] >> y[i];
        if (!cin)
            break;
        xy_t a(x[0], y[0]), b(x[1], y[1]), c(x[2], y[2]), p(x[3], y[3]);
        double pab = cross_product(a - p, b - p), pbc = cross_product(b - p, c - p), pca = cross_product(c - p, a - p);
        bool ok = pab * pbc > 0 && pbc * pca > 0;
        cout << (ok ? "YES" : "NO") << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;
double hoge(double x1,double y1,double x2, double y2){
  double a,b,c;
  a=max(x1,x2)-min(x1,x2);
  b=max(y1,y2)-min(y1,y2);
  c=(a*a)+(b*b);
  c=sqrt(c);
  return c;
}
double heron(double a,double b,double c){
  double s,S;
  s=(a+b+c)/2;
  S=s*(s-a)*(s-b)*(s-c);
  S=sqrt(S);
  return S;
}
int main(void){
  double x1,x2,x3,y1,y2,y3,xp,yp,ab,bc,ac,ap,bp,cp,abc,apb,bpc,apc,sum;
  while(cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp){
    ab=hoge(x1,y1,x2,y2);
    bc=hoge(x2,y2,x3,y3);
    ac=hoge(x1,y1,x3,y3);
    ap=hoge(x1,y1,xp,yp);
    bp=hoge(x2,y2,xp,yp);
    cp=hoge(x3,y3,xp,yp);
    abc=heron(ab,bc,ac);
    apb=heron(ap,bp,ab);
    bpc=heron(bp,cp,bc);
    apc=heron(ap,cp,ac);
    sum=apb+bpc+apc;
    if(max(abc,sum)-min(abc,sum)<=0.000000001) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
}