Compilare: user.cpp: In function ‘int main()’: user.cpp:15:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 1; k <= s.size() / 3; k++) { ^ user.cpp:17:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i + 2 * k < s.size(); i++) { ^