Challenge 1: A Mutable char Array, Modified and Reprinted — Possible Solution
====================================================================

#include <stdio.h>

int main() {
    char s[] = "hello";
    printf("%s\n", s);

    s[0] = 'H';
    printf("%s\n", s);

    return 0;
}

Output:

    hello
    Hello

WHY THIS WORKS AS AN ANSWER
------------------------------
char s[] = "hello" copies the characters into a genuinely mutable
local array (unlike char *s = "hello", which the chapter explicitly
warns points at read-only memory) -- so modifying s[0] directly is
well-defined and produces exactly the expected change, proven by
printing the array before and after.