Challenge 2: A Manual strlen, Compared Against the Real One — Possible Solution
====================================================================

#include <stdio.h>
#include <string.h>

size_t my_strlen(const char *s) {
    size_t count = 0;
    while (s[count] != '\0') {
        count++;
    }
    return count;
}

int main() {
    char test[] = "hello world";

    printf("my_strlen:   %zu\n", my_strlen(test));
    printf("real strlen: %zu\n", strlen(test));

    return 0;
}

Output:

    my_strlen:   11
    real strlen: 11

WHY THIS WORKS AS AN ANSWER
------------------------------
my_strlen implements exactly the scanning behavior the chapter
describes strlen as doing internally -- walking forward one character
at a time, counting, until it hits the '\0' sentinel -- and the two
functions agreeing on the same length (11) confirms this manual
implementation correctly reproduces the standard library's own
behavior, making concrete the chapter's point that C strings carry no
separately stored length field; both functions have to find it the
same way, by scanning.