Compilare: user.cpp: In function ‘int main()’: user.cpp:95:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 1; i <= M; ++i ) ^ user.cpp:101:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int i = 1; i <= N; ++i ) ^ user.cpp:105:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if ( val != -1 ) ^