#include "string"

void lowerCase(std::string &a);

int main()
{
setlocale(LC_ALL, "Russian");
std::string a = "Привет, МИР ЁЁЁЁЁЁ!";
lowerCase(a);
printf(a.c_str());
return 0;
}

void lowerCase(std::string &a) {
for (unsigned long i = 0; i < a.size(); i = i)
if (((a[i] <= 0xFFFFFFFFFFFFFFDF) && (a[i] >= 0xFFFFFFFFFFFFFFC0)))
a[i++] += (char)0xFFFFFFFFFFFFFF20;
else
a[i] = a[i] == 0xFFFFFFFFFFFFFFA8 ? 0xFFFFFFFFFFFFFFB8 : a[i++];
}