Compilare: user.cpp: In function ‘int main()’: user.cpp:38:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<expresie.size();){ ^ user.cpp:44:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<expresie.size() && expresie[i]>='0' && expresie[i]<='9') ^