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 <algorithm>
#include <cassert>
#include <cmath>
#include <stdio.h>
  
using namespace std;
  
//-------------------------------------------------------------------------
// geometric library
  
namespace geometry {
  
#define EPS 1E-10 ///< 0とみなすサイズ。適当
 
struct point {
    double x;
    double y;
 
    point& operator += (const point& rhs) { x += rhs.x; y += rhs.y; return *this; }
    point& operator -= (const point& rhs) { x -= rhs.x; y -= rhs.y; return *this; }
    point& operator /= (double factor) { x /= factor; y /= factor; return *this; }
    point& operator *= (double factor) { x *= factor; y *= factor; return *this; }
    bool operator == (const point& rhs) const { return (std::abs(x - rhs.x) < EPS) && (std::abs(y - rhs.y) < EPS); }
    bool operator != (const point& rhs) const { return !(*this == rhs); }
};
 
typedef point vector;
  
struct circle {
    point center;
    double radius;
};
  
struct line { // ax + by + c = 0
    double a;
    double b;
    double c;
};
 
enum rotate_dir {
    rotate_None = 0,
    rotate_CW   = 1,
    rotate_CCW  = -1
};
 
point operator + (const point& p1, const point& p2)
{
    point p(p1);
    p += p2;
    return p;
}
 
point operator / (const point& p1, double factor)
{
    point p(p1);
    p /= factor;
    return p;
}
  
point operator - (const point& p1, const point& p2)
{
    point p(p1);
    p -= p2;
    return p;
}
 
std::istream& operator >> (std::istream& is, point& p)
{
    is >> p.x >> p.y;
    return is;
}
 
///! 2点の距離
double get_distance(const point& p1, const point& p2)
{
    return sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2));
}
  
///! 2直線の交点
bool get_crosspoint(const line& l1, const line& l2, point *result)
{
    double denominator = l1.a * l2.b - l1.b * l2.a;
    if (std::abs(denominator) < EPS) {
        return false;
    }
    result->x = (l1.b * l2.c - l2.b * l1.c) / denominator;
    result->y = (l2.a * l1.c - l1.a * l2.c) / denominator;
    return true;
}
  
///! 2点の垂直2等分線
bool get_bisector(const point& p1, const point& p2, line *result)
{
    if (p1 == p2) {
        return false;
    }
    result->a = 2 * (p1.x - p2.x);
    result->b = 2 * (p1.y - p2.y);
    result->c = -(p1.y - p2.y) * (p1.y + p2.y) - (p1.x - p2.x) * (p1.x + p2.x);
    return true;
}

bool get_line(const point& p1, const point& p2, line *result)
{
    if (p1 == p2) {
        return false;
    }
    result->a = p2.y - p1.y;
    result->b = p1.x - p2.x;
    result->c = p1.y * p2.x - p1.x * p2.y;
    return true;
}
  
///! 外接円を求める
bool get_circum_circle(const point& p1, const point& p2, const point& p3, circle *result)
{
    double a = get_distance(p1, p2);
    double b = get_distance(p2, p3);
    double c = get_distance(p3, p1);
  
    // 半径の公式
    result->radius = a * b * c / sqrt((a + b + c) * (-a + b + c) * (a - b + c) * (a + b - c));
  
    line line_p1p2;
    line line_p2p3;
  
    // 頂点の垂直2等分線の交点が外心
    return get_bisector(p1, p2, &line_p1p2) &&
           get_bisector(p2, p3, &line_p2p3) &&
           get_crosspoint(line_p1p2, line_p2p3, &result->center);
}
 
double cross_product(const point& p1, const point& p2)
{
    return p1.x * p2.y - p2.x * p1.y;
}
 
///! p1-p2-p3が左右どちらの方向に折れているかを判定
rotate_dir direction(const point& p1, const point& p2, const point& p3)
{
    vector p1_p3 = p1 - p3;
    vector p2_p3 = p2 - p3;
    double cross = cross_product(p1_p3, p2_p3);
 
    if (std::abs(cross) < EPS) {
        return rotate_None;
    } else if (cross > 0) {
        return rotate_CW;
    } else {
        return rotate_CCW;
    }
}
  
// (p1s, p1e)と(p2s, p2e)の線分交差判定.EPS以下で接している場合はtrue、重なっている場合はfalse
bool intersect(const point& p1s, const point& p1e, const point& p2s, const point& p2e)
{
    assert(p1s != p1e && p2s != p2e);
    return
        (direction(p1s, p1e, p2s) != direction(p1s, p1e, p2e)) &&
        (direction(p2s, p2e, p1s) != direction(p2s, p2e, p1e));
}
 
// targetが三角形p1,p2,p3の内部にあるかどうか
bool is_inside_triangle(const point& p1, const point& p2, const point& p3, const point& target)
{
    point center_of_gravity = (p1 + p2 + p3) / 3; // 重心
 
    if (center_of_gravity == target) return true;
 
    // 重心とtargetを結んだ線分が三角形の辺と交叉するなら、点は三角形の外部にある
    bool intersect_any =
        intersect(p1, p2, center_of_gravity, target) ||
        intersect(p2, p3, center_of_gravity, target) ||
        intersect(p3, p1, center_of_gravity, target);
 
    return !intersect_any;
}

bool is_parallel(const point& p1, const point& p2, const point& p3, const point& p4)
{
    line l1, l2;
    point cross;

    if (!get_line(p1, p2, &l1) || !get_line(p3, p4, &l2)) {
        return false; // p1-p2, p3-p4で直線が作れない
    }
    return get_crosspoint(l1, l2, &cross) == false;
}

bool is_convex(const point* points, int num_points) {
    assert(num_points >= 3);

    rotate_dir base_dir = direction(points[0], points[1], points[2]);
    if (base_dir == rotate_None) {
        return false;
    }

    for (int i = 1; i < num_points; i++) {
        if (direction(points[i], points[(i+1)%num_points], points[(i+2)%num_points]) != base_dir) {
            return false;
        }
    }
    return true;
}
 
} // namespace geometry
  
//-------------------------------------------------------------------------
// solution
  
using namespace geometry;
 
int main(void)
{
    point p[4];
    char c;

    while (cin >> p[0].x >> c >> p[0].y) {
        for (int i = 1; i < 4; i++) cin >> c >> p[i].x >> c >> p[i].y;

        cout << (is_convex(p, 4) ? "YES" : "NO") << endl;
    }

    return 0;
}

C++: #include <cstdio>
#include <vector>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <sstream>
#include <cmath>
#include <climits>
#include <map>

using namespace std;

#define reep(i,f,n) for(int i=f; i<int(n); ++i)
#define rep(i,n) reep(i,0,n)

typedef vector<int> vi;

int main()
{
	double x[4], y[4];
	while(1){
		rep(i, 4){
			if(scanf("%lf,%lf,", &x[i], &y[i]) == EOF)
				return 0;
		}

		bool ok = true;
		rep(i, 4){
			if((x[(i+1)%4]-x[i])*(x[(i+1)%4]-x[(i+2)%4])+(y[(i+1)%4]-y[i])*(y[(i+1)%4]-y[(i+2)%4])<0.0){
				ok = false;
				break;
			}
		}
		puts(ok ? "YES" : "NO");
	}
}