#include <iostream>

#include <cmath>

using namespace std;

struct Point {

double x;

double y;

};

struct Vector {

Point start;

Point end;

};

Point subtract_points(const Point &p1, const Point &p2) {

Point delta;

delta.x = p1.x - p2.x;

delta.y = p1.y - p2.y;

return delta;

}

double length(const Vector &v) {

Point diff = subtract_points(v.start, v.end);

return sqrt(diff.x * diff.x + diff.y * diff.y);

}

int main() {

Vector v;

v.start.x = 1;

v.start.y = 0;

v.end.x = 2;

v.end.y = 1;

cout << "length of the vector is: " << length(v) << endl;

}