Compilare: main.cpp: In function 'int main()': main.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ main.cpp:21:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i == s.size() - 1 && ((s[i] >= 'a' && s[i] <= 'z') || (s[i] >= 'A' && s[i] <= 'Z'))) ~~^~~~~~~~~~~~~~~