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 <iostream>
#include <math.h>
using namespace std;

double length(double, double, double, double);

double triangle(double x1, double y1, double x2, double y2, double x3, double y3) {
    double a = length(x1, y1, x3, y3);
    double b = length(x2, y2, x3, y3);
    double c = length(x1, y1, x2, y2);

    double d = (a + b - c) / sqrt(a * b) / 2.0; // cos(radian)

    // cout << d << endl;

    return d;
}

double length(double x, double y, double ox, double oy) {
    return pow(x - ox, 2) + pow(y - oy, 2);
}

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

    while (cin) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3 >> xp >> yp;
        double ta = triangle(x1, y1, x2, y2, xp, yp);
        double tb = triangle(x1, y1, x3, y3, xp, yp);
        double tc = triangle(x2, y2, x3, y3, xp, yp);

        if (ta < 0 && tb < 0 && tc < 0) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }

    return 0;
}

C++: #include<iostream>
using namespace std;
bool cross(double x1,double y1,double x2,double y2,
	double x3,double y3,double x4,double y4){
		double f1,f2;
		f1=(x2-x1)*(y1-y3)+(y2-y1)*(x3-x1);
		f2=(x2-x1)*(y1-y4)+(y2-y1)*(x4-x1);
		if(f1*f2<=0){
			return true;
		}else{
			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 xg,yg;
		xg=(x1+x2+x3)/3.0;
		yg=(y1+y2+y3)/3.0;
		bool flag;
		if(cross(x1,y1,x2,y2,xp,yp,xg,yg)){
			flag=false;
		}else if(cross(x2,y2,x3,y3,xp,yp,xg,yg)){
			flag=false;
		}else if(cross(x3,y3,x1,y1,xp,yp,xg,yg)){
			flag=false;
		}else{
			flag=true;
		}
		if(flag){
			cout<<"YES"<<endl;
		}else{
			cout<<"NO"<<endl;
		}
	}
}

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

double cross(complex<double> A, complex<double> B){
	return (conj(A)*B).imag();
}

int main(){
	complex<double> Points[3], P;
	while(true){
		double x, y;
		for(int i=0; i<3; i++){
			cin >> x >> y;
			Points[i] = {x, y};
		}
		cin >> x >> y;
		P = {x, y};

		if(!cin)break;

		int sum = 0;
		for(int i=0; i<3; i++){
			sum += cross((Points[(i+1)%3]-Points[i]), (P-Points[i])) > 0;
		}
		cout << (sum==0 || sum==3? "Yes":"No") << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <vector>

using namespace std;

vector<double> simlu_eq(int N, vector<vector<double>> M){
    int i, j, k, n;
    double pivot, mul;

    for (i = 0; i < N; ++i){
        pivot = M[i][i];
        for (j = 0; j < N + 1; ++j){
            M[i][j] = (1 / pivot) * M[i][j];
        }

        for (k = i + 1; k < N; ++k){
            mul = M[k][i];
            for (n = i; n < N + 1; ++n){
                M[k][n] = M[k][n] - mul * M[i][n];
            }
        }
    }

     for (i = N -1; i > 0; --i){
         for (k = i -1; k >= 0; --k){
             mul = M[k][i];
             for (n = i; n < N + 1; ++n){
                 M[k][n] = M[k][n] - mul * M[i][n];
             }
         }
     }

    vector<double> res;
    for (i = 0; i < N; ++i){
        res.push_back(M[i][N]);
    }

    return res;
}


int main(){
    vector<double> a(2), b(2), c(2), p(2), ab(2), ac(2), ap(2);
    while(scanf("%lf %lf %lf %lf %lf %lf %lf %lf", &a[0], &a[1], &b[0], &b[1], &c[0], &c[1], &p[0], &p[1])+1){

        ab[0] = b[0] - a[0];
        ab[1] = b[1] - a[1];
        ac[0] = c[0] - a[0];
        ac[1] = c[1] - a[1];
        ap[0] = p[0] - a[0];
        ap[1] = p[1] - a[1];


    vector<vector<double>>M;
    M = vector<vector<double>>(2, vector<double>(3));
    M[0][0] = ab[0];  M[0][1] = ac[0];  M[0][2] = ap[0];
    M[1][0] = ab[1];  M[1][1] = ac[1];  M[1][2] = ap[1];
    vector<double> w = simlu_eq(2, M);

    if (w[0] > 0 && w[1] > 0 && w[0] + w[1] < 1){
        cout << "YES" << endl;
    }else{
        cout << "NO" << endl;
    }
    }
}

C++: #include <cstdio>
#include <iostream>
#include <complex>
#define rep(i,n) for(int i=0; i<(n); i++)
#define EPS 1e-10
using namespace std;

typedef complex<double> cd;

double s(cd a, cd b){
  return a.real()*b.imag()-a.imag()*b.real();
}

int main(){
  cd a[4];

  for(;;){
    rep(i,4){
      double x,y;
      if(!~scanf(" %lf %lf", &x,&y))
        return 0;
      a[i]=cd(x,y);
    }
    
    if((s(a[0]-a[3], a[1]-a[3]) > 0 && 
        s(a[1]-a[3], a[2]-a[3]) > 0 &&
        s(a[2]-a[3], a[0]-a[3]) > 0 ) ||
       (s(a[0]-a[3], a[1]-a[3]) < 0 && 
        s(a[1]-a[3], a[2]-a[3]) < 0 &&
        s(a[2]-a[3], a[0]-a[3]) < 0 ))
      printf("IN\n");
    else
      printf("OUT\n");
  }
  
  return 0;
}

C++: /*problem C*/

#include<stdio.h>

typedef struct{
	double x,y;
}point_obj;

int isClossLine(double x1,double y1,double x2,double y2,double x3,double y3,double x4,double y4){
	return ( (x1-x2)*(y3-y1)+(y1-y2)*(x1-x3))*((x1-x2)*(y4-y1)+(y1-y2)*(x1-x4));
}

int main(){
	point_obj p[5];
	int i,j;
	p[3].x=0;
	p[3].y=0;

	
		while(scanf("%lf %lf %lf %lf %lf %lf",p[0].x,p[0].y,p[1].x,p[1].y,p[2].x,p[2].y,p[4].x,p[4].y)){

			p[3].x+=p[0].x;
			p[3].y+=p[0].y;
	
			p[3].x/=3.0;
			p[3].y/=3.0;

			if(isClossLine(p[0].x,p[0].y,p[1].x,p[1].y,p[3].x,p[3].y,p[4].x,p[4].y) > 0 &&
				isClossLine(p[1].x,p[1].y,p[2].x,p[2].y,p[3].x,p[3].y,p[4].x,p[4].y) >0 &&
				isClossLine(p[0].x,p[0].y,p[2].x,p[2].y,p[3].x,p[3].y,p[4].x,p[4].y) > 0){

				printf("YES");
			}

			else{
				printf("NO");
			}
		}


		return 0;
	}