Question

My exercise says I need to write a recursive function to reverse a given string, using this prototype:
void reverse(char s[]);

The only pre-written function I’m allowed to use is strlen() from string.h library.

I have no clue where to begin from.

Answer 1

Start by having your function call another function that performs the actual recursion:

This might be more familiar recursive signature:

void reverse(char s[]) 
{
    reverse_helper(s,strlen(s));
}

void reverse_helper(char s[], int position) 
{
 // actual recursive code goes here
}

---

Since you cannot use helper functions:

This is homework and it sounds like you do not just want the answer so ask yourself the following questions.

What is your base case?

strlent(s) <= 1 // no reversing needed
at strlen(s) == 2, we need a trivial reversal with no recursion.

We know that reversing a 2 length char array is trivial, but how do you reverse a 3 length char array?

take the last char from the 3 length array and place it at the front of the reversed 2 length array.

What do a pass to my recusive calls of reverse?

a new char array that is one size smaller.