Compilare: user.cpp: In function ‘int main()’: user.cpp:68:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0; i<M.size(); ++i) ^ user.cpp:69:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=i+1; j<M.size(); ++j) ^ user.cpp:70:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k=j+1; k<M.size(); ++k) ^