C++ Calling a Function (void): 2 Coordinates of Two Points & Calculate the Distance Between The 2 Points

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

void distance (void); // with void

int main()
{
    distance();
    return 0;
}

void distance (void)
{
    double x1, x2, y1, y2, d;

    cout << "Enter value for x1: " << endl;
        cin >> x1;

    cout << "Enter value for y1: " << endl;
        cin >> y1;

    cout << "Enter value for x2: " << endl;
        cin >> x2;

    cout << "Enter value for y2: " << endl;
        cin >> y2;

    d = sqrt(((x2 - x1)*(x2 - x1)) + ((y2 - y1)*(y2 - y1)));

    cout << "The distance between the two points are: " << "d = " << d << endl;
}


/*

int main()
{
    double distance (double x1, double y1, double x2, double y2); // without void

    double x1, x2, y1, y2;

    cout << "Enter value for x1: " << endl;
        cin >> x1;

    cout << "Enter value for y1: " << endl;
        cin >> y1;

    cout << "Enter value for x2: " << endl;
        cin >> x2;

    cout << "Enter value for y2: " << endl;
        cin >> y2;

    cout << "The distance between the two points are: " << distance (x1, y1, x2, y2) << endl;
}

double distance (double x1, double y1, double x2, double y2)
{
    return sqrt (((x2 - x1)*(x2 - x1)) + ((y2 - y1)*(y2 - y1)));
}

*/