Go: package main

import (
	"bufio"
	"os"
	"strings"
	"strconv"
	"fmt"
)

func check(x, y, x1, y1, x2, y2 float64) float64 {
	return (x2-x1)*y - (y2-y1)*x + x1*y2 - x2*y1
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	a := make([]float64, 8)
	for scanner.Scan() {
		info := strings.Split(scanner.Text(), ",")
		for j := 0; j < 8; j++ {
			a[j], _ = strconv.ParseFloat(info[j], 64)
		}
		if check(a[0], a[1], a[2],a[3], a[6], a[7])*check(a[4], a[5], a[2], a[3], a[6], a[7]) < 0 && check(a[6], a[7], a[0], a[1], a[4], a[5])*check(a[2],a[3], a[0], a[1], a[4], a[5]) < 0 {
			fmt.Println("YES")	
		} else {
			fmt.Println("NO")
		}
	}
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<climits>
#include<queue>
#include<map>
#include<set>
#include<vector>
#include<list>
#include<stack>
#include<cstring>
#include<string>
#include<cmath>
using namespace std;

struct Point{
	double x,y;
	Point(){}
	Point(double _x,double _y){
		x=_x; y=_y;
	}
};

struct Line{
	double x[2],y[2];
	Line(){}
	Line(Point p,Point q){
		x[0]=p.x; x[1]=q.x;
		y[0]=p.y; y[1]=q.y;
	}
};

void RevXY(Point &p){
	swap(p.x,p.y);
}

void RevXY(Line &l){
	for(int i=0;i<2;i++) swap(l.x[i],l.y[i]);
}

bool Is_SameSide(Line l,Point p,Point q){
	//printf("%lf,%lf - %lf,%lf\np(%lf,%lf),q(%lf,%lf)\n",l.x[0],l.y[0],l.x[1],l.y[1],p.x,p.y,q.x,q.y);
	if(l.x[1]==l.x[0]){
		RevXY(l); RevXY(p); RevXY(q);
	}
	double a,b;
	a = (l.y[1]-l.y[0])/(l.x[1]-l.x[0]);
	b = l.y[0]-a*l.x[0];
	//printf("%lf,%lf - %lf,%lf : y = %lfx+(%lf)\np(%lf,%lf),q(%lf,%lf)\n",l.x[0],l.y[0],l.x[1],l.y[1],a,b,p.x,p.y,q.x,q.y);
	if((p.y-(a*p.x+b))*(q.y-(a*q.x+b))>0) return true;
	else return false;
}

int main(){
	Point S[4];
	while(scanf("%lf,%lf",&S[0].x,&S[0].y)!=EOF){
		Point sum = Point(S[0].x,S[0].y);
		for(int i=1;i<4;i++){
			scanf(",%lf,%lf",&S[i].x,&S[i].y);
			sum.x += S[i].x; sum.y += S[i].y;
		}
		bool ans=true;
		for(int i=0;i<4;i++){
			if(Is_SameSide(Line(S[i],S[(i+2)%4]),S[(i+1)%4],Point((sum.x-S[(i+1)%4].x)/3,(sum.y-S[(i+1)%4].y)/3))==true){
				ans = false;
			}
		}
		if(ans) puts("YES");
		else puts("NO");
	}
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }


vector<string> split(string str, string delim)
{
    vector<string> result;
    int cutAt;
    while( (cutAt = str.find_first_of(delim)) != str.npos )
    {
        if(cutAt > 0)
        {
            result.push_back(str.substr(0, cutAt));
        }
        str = str.substr(cutAt + 1);
    }
    if(str.length() > 0)
    {
        result.push_back(str);
    }
	return result;
}


struct P{ double x, y; };
bool operator > (P x, P y)
{ return x.x > y.x || (x.x == y.x && x.y > y.x); }


double getlen(P a, P b)
{ return sqrt(pow(a.x - b.x, 2.0) + pow(a.y - b.y, 2.0)); }

double helon(double a, double b, double c)
{
	double s = (a + b + c) / 2;

	return sqrt(s * (s - a) * (s - b) * (s - c));
}

int main()
{
	vector<P> ps(4);
	string str;

	ifstream ifs("data.txt");

	while(getline(ifs, str))
	{
		vector<string> ss = split(str, ",");

		rep(i, 4)
		{
			stringstream sts;
			sts << ss[i*2];
			sts >> ps[i].x;
			sts.clear();
			sts.str("");
			sts << ss[i*2+1];
			sts >> ps[i].y;
		}

		if(cin.eof()) break;

		

		double ab = getlen(ps[0], ps[1]);
		double bc = getlen(ps[1], ps[2]);
		double cd = getlen(ps[2], ps[3]);
		double da = getlen(ps[3], ps[0]);
		double ac = getlen(ps[2], ps[0]);
		double db = getlen(ps[1], ps[3]);

		if( abs(helon(ab, bc, ac) + helon(cd, da, ac) - helon(db, bc, cd) - helon(ab, db, da)) < EPS)
			cout << "YES" << endl;
		else
			cout << "NO" << endl;
	}

}

C++: #include<iostream>
#include<complex>
#include<stdio.h>
#include<math.h>
using namespace std;
typedef struct point{
	double x,y;
} point;
point vect(point a,point b){
	point l;
	l.x = a.x -b.x;
	l.y = a.y -b.y;
	return l;
}

double cos(point a,point b, point c){
	point p1,p2; double inner;
	p1 = vect(a,c);
	p2 = vect(b,c);
	inner = p1.x * p2.x + p1.y*p2.y;
	return inner;

}

int main(){
	char a;
	double l[4];
	while(1){
	bool ans = true;
	point p[4]; 
		for(int i=0;i<4;i++)
	if(scanf("%lf,%lf,",&p[i].x,&p[i].y) == EOF) return 0;
	
    if(cos(p[3],p[1],p[0]) < 0) ans = false;
	if(cos(p[0],p[2],p[1]) < 0) ans = false;
	if(cos(p[3],p[1],p[2]) < 0) ans = false;
	if(cos(p[2],p[0],p[3]) < 0) ans = false;
	
	if(ans == true) {cout << "YES" << endl;} else {cout << "NO" << endl; }
}


}