Program to calculate length of the string using recursion in C

#include<stdio.h> 

int find_len (char [], int);

int main ()
{
	char str[100]="Let's Learn C Programming";
	int len = 0;
    
	len = find_len (str, 0);
    
    printf ("The length of the given string is: %d\n", len);
	return 0;

}

int find_len (char str[], int index){

	static int l = 0;

	if (str[index] == '\0')
		return l;

	else
		l ++;
	find_len (str, index + 1);
}