Compilare: main.cpp: In function 'int main()': main.cpp:17:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 2; i < s.size(); i++) ~~^~~~~~~~~~ main.cpp:20:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = i; j < s.size(); j += i) ~~^~~~~~~~~~ main.cpp:27:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 2 * i; j < s.size(); j += i) ~~^~~~~~~~~~ main.cpp:35:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = i; j < s.size(); j += i) ~~^~~~~~~~~~