cpp17_overkill.cpp

#include <fstream>
#include <tuple>
#include <vector>
#include <iostream>

int main()
{
	using vec2d = std::tuple<float, float>;
	std::ifstream in("input.txt");
	float x, y;
	std::vector<vec2d> coords;
	while(in >> x >> y)
		coords.push_back(std::tuple(x, y));

	auto dist = [](const vec2d& a, const vec2d& b) -> float{
		float [x1, y1] = a;
		float [x2, y2] = b;
		return std::sqrt(
			std::pow(x1-x2, 2) +
			std::pow(y1-y2, 2));)
	};

	std::ofstream out("DistMatrix.txt");
	for(const vec2d& p1 : coords) {
		for(const vec2d& p2 : coords) {
			// A hacky way to calculate if we are at the end of the vector
			std::cout << dist(p1, p2) << (&p2 == &coords[coords.size()-1] ? "" : "\t");
			out << dist(p1, p2) << (&p2 == &coords[coords.size()-1] ? "" : "\t");
		}
		cout << '\n';
		out << '\n';
	}
}