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 <bits/stdc++.h>
using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P; //Point
namespace std {
  bool operator < (const P& a, const P& b) {
    return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
  }
}
double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
  return real(conj(a)*b);
}
struct L : public vector<P> { // Line
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};
typedef vector<P> G;
struct C {  //Circle
  P p; double r;
  C(const P &p, double r) : p(p), r(r) { }
};

int ccw(P a, P b, P c) {
  b -= a; c -= a;
  if (cross(b, c) > 0)   return +1;       // counter clockwise
  if (cross(b, c) < 0)   return -1;       // clockwise
  if (dot(b, c) < 0)     return +2;       // c--a--b on line
  if (norm(b) < norm(c)) return -2;       // a--b--c on line
  return 0;                               // a--c--b on line
}

//cross  L line  S senbun  P point
bool intersectLL(const L &l, const L &m) {
  return abs(cross(l[1]-l[0], m[1]-m[0])) > EPS || // non-parallel
         abs(cross(l[1]-l[0], m[0]-l[0])) < EPS;   // same line
}
bool intersectLS(const L &l, const L &s) {
  return cross(l[1]-l[0], s[0]-l[0])*       // s[0] is left of l
         cross(l[1]-l[0], s[1]-l[0]) < EPS; // s[1] is right of l
}
bool intersectLP(const L &l, const P &p) {
  return abs(cross(l[1]-p, l[0]-p)) < EPS;
}
bool intersectSS(const L &s, const L &t) {
  return ccw(s[0],s[1],t[0])*ccw(s[0],s[1],t[1]) <= 0 &&
         ccw(t[0],t[1],s[0])*ccw(t[0],t[1],s[1]) <= 0;
}
bool intersectSP(const L &s, const P &p) {
  return abs(s[0]-p)+abs(s[1]-p)-abs(s[1]-s[0]) < EPS; // triangle inequality
}

//distance
P projection(const L &l, const P &p) {
  double t = dot(p-l[0], l[0]-l[1]) / norm(l[0]-l[1]);
  return l[0] + t*(l[0]-l[1]);
}
P reflection(const L &l, const P &p) {
  return p + 2.0*(projection(l, p) - p);
}
double distanceLP(const L &l, const P &p) {
  return abs(p - projection(l, p));
}
double distanceLL(const L &l, const L &m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m[0]);
}
double distanceLS(const L &l, const L &s) {
  if (intersectLS(l, s)) return 0;
  return min(distanceLP(l, s[0]), distanceLP(l, s[1]));
}
double distanceSP(const L &s, const P &p) {
  const P r = projection(s, p);
  if (intersectSP(s, r)) return abs(r - p);
  return min(abs(s[0] - p), abs(s[1] - p));
}
double distanceSS(const L &s, const L &t) {
  if (intersectSS(s, t)) return 0;
  return min(min(distanceSP(s, t[0]), distanceSP(s, t[1])),
             min(distanceSP(t, s[0]), distanceSP(t, s[1])));
}
P crosspoint(const L &l, const L &m) {
  double A = cross(l[1] - l[0], m[1] - m[0]);
  double B = cross(l[1] - l[0], l[1] - m[0]);
  if (abs(A) < EPS && abs(B) < EPS) return m[0]; // same line
  if (abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m[0] + B / A * (m[1] - m[0]);
}

int main() {
  P p[4];
  while(scanf("%lf%*c%lf%*c%lf%*c%lf%*c%lf%*c%lf%*c%lf%*c%lf",&p[0].real(),&p[0].imag(),&p[1].real(),&p[1].imag(),&p[2].real(),&p[2].imag(),&p[3].real(),&p[3].imag())==8) {
    int d=ccw(p[0],p[1],p[2]);
    bool ck=true;
    for(int i=1; i<4; i++) {
      P a=p[i],b=p[(i+1)%4],c=p[(i+2)%4];
      if(d!=ccw(a,b,c)) ck=false;
    }
    if(ck) cout << "YES" << endl;
    else cout << "NO" << endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>

#define PI 3.14159265358979

using namespace std;

int main()
{
	string str;
	while(cin >> str)
	{
		double x[4],y[4];
		string keep;
		vector<string>set;
		int flag=0;
		double a[4];
		double s[4];
		int j=0;

		for(int i=0;i<=str.length();i++)
		{
			if(str[i]==',' || str.length()==i)
			{
				set.push_back(keep);
				keep.clear();
			}
			else keep+=str[i];
		}

		stringstream ss;
		for(int i=0,j=0;i<4;i++,j+=2)
		{
			ss << set[j];
			ss >> x[i];

			ss.clear();
			ss.str("");

			ss << set[j+1];
			ss >> y[i];

			ss.clear();
			ss.str("");
		}

		for(int i=0;i<4;i++)
		{
			if(x[(i+1)%4]-x[i]!=0)a[i]=(y[(i+1)%4]-y[i])/(x[(i+1)%4]-x[i]);
			else a[i]=9999999;
		}

		double sum=0;
		for(int i=0;i<4;i++)
		{
			double set[100]={};

			set[0]=fabs(a[i]*a[(i+1)%4]+1);
			set[1]=sqrt(a[i]*a[i]+1);
			set[2]=sqrt(a[(i+1)%4]*a[(i+1)%4]+1);

			if(set[1]*set[2]==0)s[i]=90;
			else s[i]=acos(set[0]/(set[1]*set[2]))*180/PI;

			sum+=s[i];
		}
		cout << sum << endl;
		if(fabs(360-sum)>=179.9999)cout << "NO" << endl;
		else cout << "YES" << endl;
	}


	return 0;
}

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++: 
#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <string>
#include <cstring>
#include <vector>
#include <map>
#include <utility>
#include <complex>
#include <stack>
#include <climits>
#include <set>
#include <numeric>

using namespace std;

typedef complex<double> P;
double sq(double x){return x*x;}

double cross(P x,P y){
	return x.real() * y.imag() - x.imag() * y.real();
}

int main(){
	double x[4],y[4];
	while(~scanf("%lf,%lf,%lf,%lf,%lf,%lf,%lf,%lf",x,y,x+1,y+1,x+2,y+2,x+3,y+3)){
		P p[4];
		for (int i = 0; i < 4; i++)
			p[i] = P(x[i],y[i]);
		bool f = true;
		for (int i = 0; i < 4; i++)
		{
			if(cross(p[i] - p[(i+1)&3],p[(i+2)&3] - p[(i+1)&3]) > 0)
				f = false;
		}
		if(f) puts("YES");
		else puts("NO");

	}

	return 0;
}