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>
#define r(i,n) for(int i=0;i<n;i++)
using namespace std;

#define EPS (1e-10)
#define equals(a,b) (fabs((a)-(b))<EPS)
//CCW??¨///////////////////////////////////
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;
/////////////////////////////////////////
class Point{
  public:
  double x,y;
  Point(double x=0,double y=0):x(x),y(y){}
  Point operator + (Point p){return Point(x+p.x,y+p.y);}
  Point operator - (Point p){return Point(x-p.x,y-p.y);}
  Point operator * (double a){return Point(a*x,a*y);}
  Point operator / (double a){return Point(x/a,y/a);}

  bool operator < (const Point &p) const{
    return x!=p.x?x<p.x:y<p.y;
  }
  bool operator == (const Point &p) const{
    return fabs(x-p.x)<EPS&&fabs(y-p.y)<EPS;
  }
};
struct Circle{
  Point c;
  double r;
};
typedef Point vect;
struct seg{Point p1,p2;};
//????????´?????????????????????
double norm(Point p){return p.x*p.x+p.y*p.y;}
//??¶????????????????????¬
double abs(Point p){return sqrt(norm(p));}
//?????????????????????????????????
double dot(Point a,Point b){
  return a.x*b.x+a.y*b.y;
}
//?????? ????????????????????????
double cross(Point a,Point b){
  return a.x*b.y-a.y*b.x;
}
//??´?????????????????¨?????\?????????????????????
bool C90(seg s1,seg s2){
  return equals(dot(s1.p2-s1.p1,s2.p2-s2.p1),0.0);
}
//????????????????????¨?????\??????????????????????????????????????????
bool C0(seg s1,seg s2){
  return equals(cross(s1.p2-s1.p1,s2.p2-s2.p1),0.0);
}
//?°???± ??????????????´???????????????
Point project(seg s,Point p){
  Point base = s.p2-s.p1;
  double r=dot(p-s.p1,base) / norm(base);
  return s.p1+base*r;
}
//????°????????????????????????????
Point reflection(seg s,Point p){
  return  p+(project(s,p)-p)*2.0;
}
//2???????????¢   ???????????????
double getDistancePP(Point a,Point b){
  return abs(a-b);
}
//??´??????????????¢(????°?)???????????????
double getDistanceLP(seg l,Point p){
  return abs(cross(l.p2-l.p1,p-l.p1)/abs(l.p2-l.p1));
}
//?????????????????¢??????????????????
double getDistanceSP(seg s,Point p){
  if(dot(s.p2-s.p1,p-s.p1)<0.0)return abs(p-s.p1);
  if(dot(s.p1-s.p2,p-s.p2)<0.0)return abs(p-s.p2);
  return getDistanceLP(s,p);
}
//????¨?????????????????¨??????????????????????????????????
int CCW(Point p0,Point p1,Point p2){
  Point a=p1-p0;
  Point b=p2-p0;
  if(cross(a,b)>EPS)return COUNTER_CLOCKWISE;
  if(cross(a,b)<-EPS)return CLOCKWISE;
  if(dot(a,b)<-EPS)return ONLINE_BACK;
  if(norm(a)<norm(b))return ONLINE_FRONT;
  return ON_SEGMENT;
}
//????????????????????????????????????????????§?\????
bool intersect(Point p1,Point p2,Point p3,Point p4){
  return(CCW(p1,p2,p3)*CCW(p1,p2,p4)<=0&&CCW(p3,p4,p1)*CCW(p3,p4,p2)<=0);
}
bool intersect(seg s1,seg s2){
  return intersect(s1.p1,s1.p2,s2.p1,s2.p2);
}
//2??????????§???¢?????\??????????????????...????????????????????????
bool squareintersect(seg s1,seg s2){
  if(s1.p2.x<s2.p1.x||s2.p2.x<s1.p1.x)return 0;
  if(s1.p2.y<s2.p1.y||s2.p2.y<s1.p1.y)return 0;
  return 1;
}
//??????????????¢?????????????????????????????§??¨???????????????
double getDistance(seg s1,seg s2){
  if(intersect(s1,s2))return 0.0;
  return min(min(getDistanceSP(s1,s2.p1),getDistanceSP(s1,s2.p2)),
    min(getDistanceSP(s2,s1.p1),getDistanceSP(s2,s1.p2)));
}
//??????????????????????????????(?´????????`)
Point getCrossPoint(seg s1,seg s2){
  Point base=s2.p2-s2.p1;
  double d1=abs(cross(base,s1.p1-s2.p1));
  double d2=abs(cross(base,s1.p2-s2.p1));
  double t=d1/(d1+d2);
  return s1.p1+(s1.p2-s1.p1)*t;
}
//?????¨??´???????????????2??????
seg getCrossPoint(Circle c,seg l){
  //assert(intersect(cc,l));
  Point pr=project(l,c.c);
  Point e=(l.p2-l.p1)/abs(l.p2-l.p1);
  double base =sqrt(c.r*c.r-norm(pr-c.c));
  seg pp;pp.p1=(pr+e*base);pp.p2=(pr-e*base);
  return pp;
}
//????´???°2D///////////A???)///////////
typedef complex<double> comp;
typedef vector<comp> cvec;
//????´???????
double dot(comp a,comp b){return real(b*conj(a));}
//????´???????
double cross(comp a,comp b){return imag(b*conj(a));}
double Area(cvec &a){
  double b=0;int n=a.size();
  for(int i=0;i<n;i++)
    b+=cross(a[i],a[(i+1==n?0:i+1)]);
  return abs(b/2.0);
}
////how to use(exp)/////////////////////
//  double a,b; cvec t; cin>>n;       //
// while(n--){                        //
//    cin>>a>>b;                      //
//    t.push_back(comp(a,b));         //
//  }printf("%.11f\n",Area(t));       //
////////////////////////////////////////
//???????£????????????¢??????????????¢??????????????????????????\????????????????????§???????????£???????????????????????????????????§?????????????????????
int intersectCC(Circle a,Circle b){
  double dist=abs(a.c-b.c);
  if(dist>a.r+b.r+EPS)return 4;
  if(dist>a.r+b.r-EPS)return 3;
  if(dist>abs(a.r-b.r)+EPS)return 2;
  if(dist>abs(a.r-b.r)-EPS)return 1;
  return 0;
}
seg scan(){
  seg a;
  scanf("%lf%lf%lf%lf",&a.p1.x,&a.p1.y,&a.p2.x,&a.p2.y);
  return a;
}
int main(){
  Circle o,q;
  Point a,b,c,d;
  while(cin>>a.x>>a.y>>b.x>>b.y>>c.x>>c.y>>d.x>>d.y){
    int q1=CCW(a,b,d),q2=CCW(b,c,d),q3=CCW(c,a,d);
    if(q1==q2&&q1==q3)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
}

C++: #include <stdio.h>
#include <math.h>

void swap(double *a, double *b)
{
  double tmp = *a;
  *a = *b;
  *b = tmp;
}

double angle(double x, double y)
{
  double angle = acos(x/sqrt(x*x+y*y));
  if(y<0){
    angle = 2*M_PI-angle;
  }

  return angle;
}

int main(void)
{
  double x1,y1,x2,y2,x3,y3,xp,yp;
  while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3, &xp, &yp) != EOF){
    double alpha = angle(x1-xp, y1-yp);
    double beta = angle(x2-xp, y2-yp);
    double gamma = angle(x3-xp, y3-yp);
    
    if(alpha>beta){
      swap(&alpha, &beta);
    }
    if(beta>gamma){
      swap(&beta, &gamma);
    }
    if(alpha>beta){
      swap(&alpha, &beta);
    }

    if(beta-alpha<M_PI && gamma-beta<M_PI && gamma-alpha>M_PI){
      printf("YES\n");
    }else{
      printf("NO\n");
    }
  }

  return 0;
}