What is the time complexity of the recursive implementation used to convert a decimal number to its binary equivalent?

[answerhappygod]

#include<stdio.h>
int arr[31], len = 0;
void recursive_dec_to_bin(int n)
{
if(n == 0 && len == 0)
{
arr[len++] = 0;
return;
}
if(n == 0)
return;
arr[len++] = n % 2;
recursive_dec_to_bin(n/2);
}
a) O(1)
b) O(n)
c) O(n2)
d) O(logn)