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 FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(b) - 1;i>=(a);i--)
#define REP(i,n) for(int i=0;i<(n);i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)

#define PB push_back
#define INF INT_MAX/3
#define ALL(a) (a).begin(),(a).end()
#define CLR(a) memset(a,0,sizeof(a))

typedef long long int ll;

using namespace std;

int main(){

    double x[4],y[4];
    while(true){
	REP(i,4) {
	    cin >> x[i];
	    if(cin.eof()) return 0;
	    cin >> y[i];
	}
	double s,t;
	bool flg = false;
	REP(i,1e6){
	    s = ((double)i/1e6);
	    t = (double)1 - s;
	    double x1 = s * (x[2] - x[0]) + t * ( x[1] - x[0]);
	    double y1 = s * (y[2] - y[0]) + t * ( y[1] - y[0]);
	    double x2 = x[3] - x[0];
	    double y2 = y[3] - y[0];
	    double dotpro = (  (  (x1 * x2 + y1 * y2 )*(x1 * x2 + y1 * y2 ) )  /( (x1*x1 + y1*y1)*(x2*x2 + y2*y2))); 
	    //cout << dotpro << endl;
	    if(  1 - dotpro  <= 0.01  ){
		    flg = true;
		    break;
	    }
	}
	if(flg) cout << "YES" << endl;
	else cout << "NO" << endl;

    }

    return 0;
}

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

int main(){
  float x1,y1,x2,y2,x3,y3,xp,yp;
  float a1,b1,a2,b2,A,B;
  while(cin>>x1>>y1>>x2>>y2>>x3>>y3>>xp>>yp){
    a1=x2-x1;
    a2=y2-y1;
    b1=x3-x1;
    b2=y3-y1;
    xp=xp-x1;
    yp=yp-y1;
    A=(b1*yp-b2*xp)/(a2*b1-a1*b2);
    B=(a2*xp-a1*yp)/(a2*b1-a1*b2);
    if(A+B<1&&A>0&&B>0) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
  }
  return 0;
}

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

typedef complex<double> Point;

double cross(Point a, Point b){
    return (conj(a)*b).imag();
}

int main(){
    Point V[3], P;
    while(!cin.eof()){
        for(int i=0; i<3; i++){
            double x, y; cin >> x >> y;
            V[i] = {x, y};
        }
        double x, y; cin >> x >> y;
        P = {x, y};
        
        int sum = 0;
        for(int i=0; i<3; i++){
            double a = cross(V[(i+1)%3]-V[i], (P-V[i]));
            sum += a/abs(a);
        }
        cout << (abs(sum) == 3? "YES": "NO") << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(b) - 1;i>=(a);i--)
#define REP(i,n) for(int i=0;i<(n);i++)
#define RREP(i,n) for(int i=n-1;i>=0;i--)

#define PB push_back
#define INF INT_MAX/3
#define ALL(a) (a).begin(),(a).end()
#define CLR(a) memset(a,0,sizeof(a))

typedef long long int ll;

using namespace std;

int main(){

    double x[4],y[4];
    while(true){
	REP(i,4) {
	    cin >> x[i];
	    if(cin.eof()) return 0;
	    cin >> y[i];
	}
	double s,t;
	double m = 0;
	bool flg = false;
	    double x1[] =  {x[2] - x[0],  x[1] - x[0]};
	    double y1[] = { y[2] - y[0] , y[1] - y[0]};
	    double x2 = x[3] - x[0];
	    double y2 = y[3] - y[0];
	    REP(i,1e3){
		REP(j,1e3){
		s = (double)i / 1e3;
		t = (double)j / 1e3;
		if(s * x1[0] + t * x1[1] - x2 < 1e-5 && s * y1[0] + t * y1[1] - y2 < 1e-5){
		    flg = true;
		    break;
		}
	    }
		if(flg) break;
	    }
	    if(flg) cout << "YES" << endl;
	    else cout << "NO" << endl;

    }

    return 0;
}

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

using namespace std;

int main(){
	double x1,x2,x3,y1,y2,y3,xp,yp;
	double calc1,calc2,calc3;

	while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3,&xp,&yp)!=EOF){
		calc1 = (x2-x1)*(yp-y1)-(y2-y1)*(xp-x1);
		calc2 = (x3-x2)*(yp-y2)-(y3-y2)*(xp-x2);
		calc3 = (x1-x3)*(yp-y3)-(y1-y3)*(xp-x3);

		if((calc1>0&&calc2>0&&calc3>0) || (calc1<0&&calc2<0&&calc3<0)){
			printf("YES\n");
		}else{
			printf("NO\n");
		}
	}
    return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <vector>
#include <math.h>
#include <set>
#include <map>
#include <string>
#include <stack>
#include <queue>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <bitset>
#include <complex>
#define _USE_MATH_DEFINES
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> plglg;
typedef tuple<int, int, int> tiii;
typedef tuple<ll, ll, ll> tlglglg;
typedef complex<double> xy_t;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
double pi = 3.141592653589793;
ll mod = 1000000007;
int intmax = 2147483647;
int intmin = -2147483648;
ll llmax = 9223372036854775807;
ll llmin = -9223372036854775807;
ll inf = llmax / 2;
double eps = 1e-11;

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

int main() {
    double x[4], y[4];
    while (true) {
        for (int i = 0; i < 4; i++) {
            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 d[3];
        d[0] = cross_product(a - p, b - p);
        d[1] = cross_product(b - p, c - p);
        d[2] = cross_product(c - p, a - p);
        if (d[0] * d[1] > 0 && d[1] * d[2] > 0) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
}

C++: #include<iostream>

double cross( double x1, double y1, double x2, double y2 )
{
	return x1 * y2 - x2 * y1;
}

int main()
{
	double x[3], y[3], xp, yp;

	while( std::cin >> x[0] >> y[0] )
	{
		for( int i = 1; i != 3; ++i )
			std::cin >> x[i] >> y[i];
		std::cin >> xp >> yp;

		bool s, f = true;
		for( int i = 0; i != 3; ++i )
		{
			double t = cross( x[( i + 1 ) % 3] - x[i], y[( i + 1 ) % 3] - y[i], xp - x[i], yp - y[i] );

			if( !i )
			{
				if( t > 0 )
					s = true;
				else
					s = false;
			}

			f &= ( t < 0 ) ^ s;
		}

		if( f )
			std::cout << "YES" << std::endl;
		else
			std::cout << "NO" << std::endl;
	}

	return 0;
}

C++: #include <iostream>


class vector_t {
public:
  double x;
  double y;
  double z;

public:
  vector_t(double x = 0, double y = 0, double z = 0) : x(x), y(y), z(z) {};

public:
  vector_t operator^(const vector_t& v) const {
    return vector_t(y * v.z - z * v.y,
                    z * v.x - x * v.z,
                    x * v.y - y * v.x);
  };
};


class point_t {
public:
  double x;
  double y;
  double z;
  double w;

public:
  point_t(double x = 0, double y = 0, double z = 0, double w = 1) : x(x), y(y), z(z), w(w) {};
  
public:
  vector_t operator-(const point_t& p) const {
    return vector_t(x - p.x, y - p.y, z - p.z);
  };
};


int main(int argc, char** argv)
{
  double x1, y1, x2, y2, x3, y3, xp, yp;

  while (std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp) {
    point_t p1(x1, y1);
    point_t p2(x2, y2);
    point_t p3(x3, y3);
    point_t p (xp, yp);

    if (((p2 - p1) ^ (p - p1)).z > 0 &&
        ((p3 - p2) ^ (p - p2)).z > 0 &&
        ((p1 - p3) ^ (p - p3)).z > 0) {

      std::cout << "YES" << std::endl;
    }
    else {
      std::cout << "NO" << std::endl;
    }
  }
}