/in/foo.cc: In function 'int main()':
/in/foo.cc:13:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < str.size(); ++i){
                   ~~^~~~~~~~~~~~
/in/foo.cc:14:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    if (str[i] >= 'a' && str[i] <= 'z' || str[i] >= 'A' && str[i] <= 'Z')