Бесконечный ввод

#include <iostream>
using namespace std;
int main() {
    setlocale(LC_ALL, "Rus");
    long double x1, x2, x3, x4, y1, y2, y3, y4;
    cout << "x1="; cin >> x1; 
    cout << "y1="; cin >> y1;
    cout << "x2="; cin >> x2;
    cout << "y2="; cin >> y2;
    cout << "x3="; cin >> x3;
    cout << "y3="; cin >> y3;
    cout << "x4="; cin >> x4;
    cout << "y4="; cin >> y4;
      long double a = (x2 - x1) * (y2 - y1) - (x3 - x2) * (y3 - y1);
      long double b = (x3 - x1) * (y4 - y3) - (x4 - x3) * (y3 - y1);
      long double c = (x4 - x1) * (y2 - y4) - (x2 - x4) * (y4 - y1);
        if ((a >= 0 && b >= 0 && c >= 0) || (a <= 0 && b <= 0 && c <= 0))
            cout << "Внутри";
        else
            cout << "Снаружи";
   
    return 0;
}

#include <iostream>
int main()
{
    setlocale(LC_ALL, "Rus");
    double x[4], y[4];
    bool flg = false;
    while (true)
    {
        for (int i = 0; i < 4; i++)
        {
            std::cout << "x" << i + 1 << " = "; std::cin >> x[i];
            std::cout << "y" << i + 1 << " = "; std::cin >> y[i];
            if (x[i] == 0.0 && y[i] == 0.0) { flg = true; break; }
        }
        if (flg) { break; }
        double a = (x[1] - x[0]) * (y[1] - y[0]) - (x[2] - x[1]) * (y[2] - y[0]);
        double b = (x[2] - x[0]) * (y[3] - y[2]) - (x[3] - x[2]) * (y[2] - y[0]);
        double c = (x[3] - x[0]) * (y[1] - y[3]) - (x[1] - x[3]) * (y[3] - y[0]);
        if ((a >= 0.0 && b >= 0.0 && c >= 0.0) || (a <= 0.0 && b <= 0.0 && c <= 0.0))
            std::cout << "Внутри" << std::endl;
        else
            std::cout << "Снаружи" << std::endl;
    }
    return 0;
}