Challenge 1: Sorting a Vector and Printing With an Explicit Iterator Loop — Possible Solution
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#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> nums = {40, 10, 30, 20, 50};

    std::sort(nums.begin(), nums.end());

    for (auto it = nums.begin(); it != nums.end(); ++it) {
        std::cout << *it << std::endl;
    }

    return 0;
}

Output:

    10
    20
    30
    40
    50

WHY THIS WORKS AS AN ANSWER
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std::sort(nums.begin(), nums.end()) sorts the vector in place using
only its begin/end iterators, with no knowledge of what specific
container type it's operating on -- exactly the chapter's own
"algorithms don't care which container" point. The printing loop uses
the explicit it != nums.end() / ++it / *it pattern rather than a
range-based for, matching what the chapter states that syntax actually
expands to underneath.