Compilare: user.cpp: In function ‘int main()’: user.cpp:14:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^ user.cpp:17:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^ user.cpp:19:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int l = 1; l < s.size(); ++l) { ^ user.cpp:20:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i + l < s.size(); ++i) { ^