convert uppercase to lowercase in c++ string code example

Example 1: convert characters to lowercase c++

str[i] = tolower(str[i]);

Example 2: convert all strings in vector to lowercase or uppercase c++

for(std::string &s : stringVector){
    std::transform(s.begin(), s.end(), s.begin(), 
        [](char c){ return std::toupper(c); }); // for lowercase change "toupper" -> "tolower" 
}