Compilare: user.cpp: In function ‘int main()’: user.cpp:16:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (u=0;u<v.size();u++) ^ user.cpp:45:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (u=e+1;u<=v.size();u++) ^ user.cpp:47:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (v[u]>='0'&&v[u]<='9'&&u!=v.size()) ^ user.cpp:53:53: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (v[u]=='+' or v[u]=='-' or u==v.size()) ^