Обработка содержимого STL vector

#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
 
template<typename T>
std::ostream &operator<<(std::ostream &out, const std::vector<T> &v) {
    for (const auto &i : v) {
        out << i << " ";
    }
    return out;
}
 
int main() {
 
    std::vector<double> a{1.2, 2.3, 3.4, 4.5, 5.6, 6.7, 7.8, 8.9, 9.10, 10.11};
    std::vector<double> b = a;
 
    std::cout << std::fixed << std::setprecision(2) << a << '\n' << b << '\n'
              << "Compare: " << std::boolalpha
              << std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end()) << "\n";
 
    b[3] = b[2] + 0.01;
 
    std::cout << std::fixed << std::setprecision(2) << a << '\n' << b << '\n'
              << "Compare: " << std::boolalpha
              << std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end(), std::greater<>()) << "\n";
 
    double value = 5.6;
 
    auto lower = std::lower_bound(a.begin(), a.end(), value);
    auto upper = std::upper_bound(a.begin(), a.end(), value);
 
    std::cout << "Lower bound: " << *lower << "\nUpper bound: " << *upper << "\n";
 
    return 0;
}