#include <cctype>
#include <iostream>
#include <string>

int main()
{
  std::string s = "Hallo, Welt";

  for (unsigned i = 0; i < s.size(); ++i)
  {
    s[i] = i%2 ? std::tolower(s[i]) : std::toupper(s[i]); 
  }
  std::cout << s << '\n';
}