#include <iostream>
#include <string>
#include <algorithm>
 
int main() {
    std::string s1 { "azerty" };
    std::string s2 { "123456" };
    std::swap_ranges(begin(s1), begin(s1) + 3, begin(s2));
    std::cout << s1 << std::endl;
    std::cout << s2 << std::endl;
}