Is using strlen() in the loop condition slower than just checking for the null character?

Question

I have read that use of strlen is more expensive than such testing like this:

We have a string x 100 characters long.

I think that<

Answer 1

I guess the compiler could optimize (check Gregory Pakosz comment) your first for loop so that you would be like this:

int len = strlen(x);
for (int i = 0; i < len; i++)

Which is still O(n).

Anyway, I think your second for loop will be faster.