Working with coordinates x y - c++

Question

I need to read from a file coordinates of points. The file looks like this:
x0 y0
x1 y1
....
Then find center and diameter of the smallest enclosing circle. But I stucked in the beginning.
I don't know how to hold coordinates and decided to choose array of structures. I've read coordinates into structure.
I'm going to make 4 conditions:
1 - There is one point and you can't find the smallest enclosing circle.
2 - There are 2 points. Now the task is to find distance between them and its center.
3 - There are 3 points.
4 - More than 3 points. Use of special algorithm
I tried to use vector. I don't know how to use my points (elements of vector) later in functions etc.
#include "stdafx.h"
#include <stdio.h>
#include <fstream>
#include <iostream>
#include <vector>
using namespace std;
// Distance
float distance(){
return sqrt((point[0].x * point[1].x) + (point[0].y * point[1].y));
}
struct Points
{
float x, y;
};
int _tmain(int argc, _TCHAR* argv[])
{
vector<Points> point;
Points tmp;
ifstream fin("Points.txt");
if (!fin.is_open())
cout << "Cannot open the file \n";
else{
while (fin >> tmp.x >> tmp.y){
point.push_back(tmp);
cout << tmp.x << tmp.y << endl;
}
fin.close();
}
return 0;
}

Answer 1

I would name the struct something like Point rather than Points,
since a single instance of the struct holds only one pair of x,y coordinates.
Then a suitable distance function might be something like
float distance(const Point& point1, const Point& point2)
{
return sqrt((point1.x * point2.x) + (point1.y * point2.y));
}
You can get the distance between any two points in your input set like this:
distance(point[i], point[j])
You might also want to measure the distances from your input points to
a point that is not in the set, such as a point where you think the center
of the circle might be. For example,
distance(point[i], candidate_center_of_circle)
If it were my code, I would likely make Point a class and give it a
member function for distance so that I could write something like
candidate_center_of_circle.distanceTo(point[i])
By the way, I might name the variable points rather than point
because it is a vector that holds multiple instances of Point.
If you intend to write things like point[i] a lot you might not like
points[i], but if you are mostly going to make STL iterators over the vector
then you would have something like this:
for (std::vector<Point>::const_iterator it = points.begin(); it != points.end(); ++it)