Compilare: user.cpp: In function ‘int main()’: user.cpp:38:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); ++i){ ^ user.cpp:52:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); ++i){ ^ user.cpp:37:9: warning: unused variable ‘i’ [-Wunused-variable] int i, k=0, x=0; ^