Compilare: main.cpp: In function 'std::vector<std::vector<int> > matrixProduct(std::vector<std::vector<int> >&, std::vector<std::vector<int> >&)': main.cpp:17:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 17 | for(int j = 0; j<m2.size(); j++){ | ~^~~~~~~~~~