Compilare: user.cpp: In function ‘std::vector<std::vector<int> > mult(const std::vector<std::vector<int> >&, const std::vector<std::vector<int> >&)’: user.cpp:38:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < a.size(); ++i ) ^ user.cpp:39:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int j = 0; j < a[0].size(); ++j ) ^ user.cpp:40:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int k = 0; k < b[0].size(); ++k ) ^ user.cpp:42:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < a.size(); ++i ) ^ user.cpp:43:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int k = 0; k < b[0].size(); ++k ) ^