double foo(double *a, int n) {
  double x = 0.0;
  double y = 0.0;
  for (int i = 0; i < n; i += 2) {
    x += a[i];
    y += a[i + 1];
  }
  return x * y;
}

double bar(double *a, unsigned n) {
  double x = 0.0;
  double y = 0.0;
  for (unsigned i = 0; i < n; i += 2) {
    x += a[i];
    y += a[i + 1];
  }
  return x * y;
}