Compilare: main.cpp: In function 'int main()': main.cpp:24:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s1.size(); ++i) { ~~^~~~~~~~~~~ main.cpp:30:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ main.cpp:35:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i + len < s.size() && i >= len && s[i - len] == s[i + len]) ~~~~~~~~^~~~~~~~~~