how to convert uppercase char to lowercase in c++ code example

Example 1: convert characters to lowercase c++

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

Example 2: convert from uppercase to lowercase c++

int i = 0;
    while(str[i])
    {
        if(str[i] == std::toupper(str[i]) && std::isalpha(str[i]) == 1024)
        str[i]+= 32;
        ++i;
    }