Compilare: main.cpp: In function 'mat operator*(const mat&, const mat&)': main.cpp:25:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare] 25 | for (int i = 0; i < a.size(); i++) { | ~~^~~~~~~~~~ main.cpp:26:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 26 | for (int j = 0; j < b[0].size(); j++) { | ~~^~~~~~~~~~~~~ main.cpp:28:31: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 28 | for (int k = 0; k < a[0].size(); k++) { | ~~^~~~~~~~~~~~~