Compilare: user.cpp: In function ‘int main()’: user.cpp:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (unsigned i=0; i!=N; ++i) ^ user.cpp:13:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (unsigned j=0; j!=M; ++j) ^ user.cpp:16:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (unsigned i=1; i!=M; ++i) { ^ user.cpp:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (unsigned i=1; i!=N; ++i) ^ user.cpp:21:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (unsigned j=0; j!=M; ++j) { ^