Compilare: main.cpp: In function 'std::vector<std::vector<int> > multiply_matrix(std::vector<std::vector<int> >&, std::vector<std::vector<int> >&)': main.cpp:11:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 11 | for (int i = 0; i < a.size(); i++) { | ~~^~~~~~~~~~ main.cpp:12:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 12 | for (int j = 0; j < b[0].size(); j++) { | ~~^~~~~~~~~~~~~ main.cpp:13:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 13 | for (int k = 0; k < b.size(); k++) { | ~~^~~~~~~~~~