Given 2^n, find n using logarithm

Question

Given a integer(2^n) which is power of 2, I want to find out n, the index value using logarithm. The formula to find index is : log(number) / log(2). Following is the code snipp

Answer 1

I am only answering half of your question, because it is not necessary to use logs to solve this. An easy way is to use this:

unsigned long long a = 0x8000000000000000ULL;
int n = 0;
while (a >>= 1) n++;
printf("%d\n", n);

Output:

63

Converting to logs and divding may cause loss of significance, in which case you should use round. You use the word "submit", so it was an online challenge that failed? What exactly did you print? (in this case) 63.000000? That would be got from the default format of %f.