通过递归的幂函数

Question

The implementation should compute a number to the nth power using recursion, however, every call to itself, keeps "nb" unchanged, while power decrements. I've tried using a accumulator variable but this reinitializes to default with every repeated call. Is there a way to save nb * nb to nb, without adding an extra parameter? or losing the base value?

When I run ft_recursive_power(3, 10); in ac visualizer (ctutor) and pass it these arguments, it displays that nb remains 3 throughout the execution, and returns 177147, while it should accumulate the multiplication and return 59049. Or am I missing something?

int   ft_recursive_power(int nb, int power)
{
  // 0 to the 0th case
  if (power == 0 && nb == 0)
    return (1);
  // recursive case
  if (power > 0)
    return (nb * ft_recursive_power(nb, power - 1));
  return (nb);
}

Answer 1

You're getting an incorrect result because your base case is wrong.

The value 177147 is 3 ¹¹ as opposed to 3 ¹⁰ , which means you're multiplying one extra time. That happens because you return nb in the base case when power is 0.

When raising a number to the 0 power the result is 1, so your base case should be 1.

int   ft_recursive_power(int nb, int power)
{
  // 0 to the 0th case
  if (power == 0 && nb == 0)
    return 1;
  // recursive case
  if (power > 0)
    return nb * ft_recursive_power(nb, power - 1);
  return 1;
}

Answer 2

Here your problem:

if (power == 0 && nb == 0)

should be replaced by

if (power == 0)

and added case (nb == 0) as well

if (nb == 0)

The function should work for negative power as well, so I suggested change the return type to float.

It is my solution:

float   ft_recursive_power(int nb, int power)
{
    // 0 to the 0th case
    if (power == 0)
        return 1;
    if (nb == 0)
        return 0;

    // recursive case
    // power is positive
    if (power > 0)
        return (nb * ft_recursive_power(nb, power - 1));

    // mean power is negative
    else
        return (ft_recursive_power(nb, power + 1) / nb);
}