Найти точки которые находятся внутри окружности

#include <iostream>
#include <cmath>
 
    using namespace std;
 
double distance(double x1, double y1, double x2, double y2) {
    return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
}
 
int main() {
    int k = 0;
    int choice;
    double x0, y0, r;
    double x1, y1, x2, y2, x3, y3;
    back:
    cout << "Enter a circle center:\n";
    cout << "x0 = ";
    cin >> x0;
    cout << "y0 = ";
    cin >> y0;
    cout << "Enter a circle radius:\n";
    cout << "r = ";
    cin >> r;
    cout << "Enter three point coords:\n";
    cout << "x1 = ";
    cin >> x1;
    cout << "y1 = ";
    cin >> y1;
    cout << "x2 = ";
    cin >> x2;
    cout << "y2 = ";
    cin >> y2;
    cout << "x3 = ";
    cin >> x3;
    cout << "y3 = ";
    cin >> y3;
    if (distance(x0, y0, x1, y1) < r)
        k++;
    if (distance(x0, y0, x2, y2) < r)
        k++;
    if (distance(x0, y0, x3, y3) < r)
        k++;
    cout << "Output of the program:\n" << k << "\n";
    cout << "\nDo you want to exit?\n";
    cout << "1 - Yes\n";
    cout << "2 - No\n";
    cout << "Your choice: ";
    cin >> choice;
    if (choice == 2) {
        system("cls");
        goto back;
    } else {
        exit(0);
    }
    system("pause");
    return 0;
}