Units in C++ using user-defined literals

units.cpp

// Units in C++ with user-defined literals
// g++ units.cpp -std=c++11 && ./a.out

#include <assert.h>
#include <iostream>
using namespace std;

long double operator "" _km(long double x) {
  return 0.6213725 * x;
}

// 🇺🇸
long double operator "" _mi(long double x) {
  return x;
}

int main() {
  long double delta = 0.00001;
  assert((1.60934_km - 1.0_mi) < delta);
  cout << "1.60934_km ≈ 1.0_mi" << endl;
  return 0;
}