Точка в треугольнике

#include <iostream>
 
struct point
{
    double x;
    double y;
};
 
bool foo(point p[])
{
    int a = (p[1].x - p[0].x) * (p[2].y - p[1].y) * (p[1].y - p[0].y),
    b = (p[2].x - p[0].x) * (p[3].y - p[2].y) * (p[2].y - p[0].y),
    c = (p[3].x - p[0].x) * (p[1].y - p[2].y) * (p[3].y - p[0].y);
 
    return (a >= 0 && b >= 0 && c >= 0) ||
                (a <= 0 && b <= 0 && c <= 0)? 1 : 0;
}
 
bool prov(point p[])
{
    return p[1].x == p[2].x && p[2].x == p[3].x? 0 :
                p[1].y == p[2].y && p[2].y == p[3].y? 0 : 1;
}
 
int main()
{
    const size_t n = 4;
    point p[n];
 
    std::cout << "\n\nEnter coord point: ";
    for(size_t i = 0; i < n; ++i)
    {
        if(i > 0)
            std::cout << "\n\nEnter tringale coord " << i << ": ";
 
        std::cout << "\n\nx" << i << " -> ";
        std::cin >> p[i].x;
        std::cout << "\n\ny" << i << " -> ";
        std::cin >> p[i].y;
    }
 
    if(prov(p))
    {
        if(foo(p))
           std::cout << "\n\tYes" << std::endl;
 
        else
           std::cout << "\n\tNo" << std::endl;
    }
 
    else
        std::cout << "\n\tTringale not found" << std::endl;
 
    return 0;
}

bool foo(point p[])
{
    int a = (p[1].x - p[0].x) * (p[2].y - p[1].y) - (p[2].x - p[1].x) * (p[1].y - p[0].y),
    b = (p[2].x - p[0].x) * (p[3].y - p[2].y) - (p[3].x - p[2].x) * (p[2].y - p[0].y),
    c = (p[3].x - p[0].x) * (p[1].y - p[3].y) - (p[1].x - p[3].x) * (p[3].y - p[0].y);
 
    return (a >= 0 && b >= 0 && c >= 0) ||
                (a <= 0 && b <= 0 && c <= 0)? 1 : 0;
}

#include <iostream>
#include <cmath>
using namespace std;
 
struct point
{
   int x;
   int y;
};
 
int area(point a, point b, point c)
{
   return abs((a.x - c.x)*(b.y - c.y) + (b.x-c.x)*(c.y-a.y));
}
 
int main()
{
   /////////////////////////////////////////////////////////////////////////////
   point a, b, c, d;
   cin >> a.x >> a.y;
   cin >> b.x >> b.y;
   cin >> c.x >> c.y;
   cin >> d.x >> d.y;
   /////////////////////////////////////////////////////////////////////////////
   if (area(a, b, c) == area(a, b, d) + area(a, d, c) + area(b, d, c))
      cout << "In\n";
   else 
      cout << "Out\n";
   /////////////////////////////////////////////////////////////////////////////
   return 0;
}

if (fabs(a - b) < 1E-8)
    std::cout << "Равны";
else
    std::cout << "Не равны";