Challenge 1: Modifying a Variable Through a Reference — Possible Solution
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#include <iostream>

int main() {
    int value = 10;
    int &ref = value;

    ref = 50;

    std::cout << value << std::endl;

    return 0;
}

Output:

    50

WHY THIS WORKS AS AN ANSWER
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ref is bound to value at declaration (per the chapter, a reference is
an alias, not a separate object), so assigning to ref through ref = 50
is exactly the same operation as assigning directly to value -- there
is no separate memory location involved the way there would be with a
pointer needing a dereference. Printing value directly afterward
confirms the change happened through the alias, using std::cout as
required rather than printf.