#include <iostream>
#include <string>

int main() {
	std::string const UPPER = "HELLO, WORLD!";
	std::cout << "UPPER: " << UPPER << "\n";
	
	std::string lower = UPPER;
	for (char* begin = const_cast<char*>(lower.data()),
	         * end = begin + lower.size();
         begin != end;
         ++begin)
	{
		*begin = std::tolower(*begin);
	}
	std::cout << "lower: " << lower << "\n";
	std::cout << "UPPER: " << UPPER << "\n";
	return 0;
}