Compilare: user.cpp: In function ‘int main()’: user.cpp:59:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=2;j<s.size();j++) ~^~~~~~~~~ user.cpp:69:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<expr.size();i++) ~^~~~~~~~~~~~ user.cpp:80:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<elem.size();i++) ~^~~~~~~~~~~~