double power(double number, int pow){
  double result; 

  printf("power(%lf,%i)\n", number, pow);   // reveals the computation

  if (pow == 0)
    result = 1.0;
  else if (pow > 0 && even(pow))
    result = sqr(power(number,pow/2));
  else if (pow > 0 && odd(pow))
    result = number * power(number, pow - 1);
  else 
    result = 1.0 / power(number, -pow);

  return result;
}