Compilare: user.cpp: In function ‘int main()’: user.cpp:45:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(;i<expresie.size();){ ^ user.cpp:51:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<expresie.size() && expresie[i]>='0' && expresie[i]<='9') ^