#include <vector>
#include <string>
#include <iostream>
void doubler(std::vector<std::string>& vec) {
for(auto& element: vec) {
element += element;
}
}
void showVec(const std::vector<std::string>& vec) {
for(const auto& element: vec) {
std::cout << element << '\n';
}
}
int main() {
std::vector<std::string> vec{"Ba", "Be", "Bi", "Bo", "Bu"};
doubler(vec);
showVec(vec);
}